How to build electronics projects cheaply: a BOM-first method

The way to build electronics projects cheaply is to decide what the project needs before you buy anything, then spend money only on the few parts where quality changes the outcome. Write a bill of materials (BOM) first. Pick generic parts for everything that is only there to do a job. Pay more for power, lithium cells and anything connected to the wall. Then buy the cheap leftovers in packs, in one order, instead of one part at a time.

None of this is clever, but it separates a project that costs what you expected from one bloated by six small orders, two wrong boards and a starter kit you never touch. Below is the method, then one worked example: an ESP32 sensor node that reports temperature, humidity and pressure.

Write the BOM before you open a shop tab

A BOM is a list of every part the project needs, with enough detail to buy it. For a hobby project it can live in a text file. What matters is that it exists before the first order.

Writing it forces three questions. What does each part have to do? Which jobs are delicate and which are routine? How many do you need, as opposed to what a listing happens to sell?

For each line, write down the function in plain words: "reads temperature and humidity over I2C at 3.3 V", not "BME280". The model name is a means to an end. If you write only the name, you will search only for the name, and you will skip equally good parts sold under another label. PartLark's why-use page describes the same idea: a generic board that does the job is a legitimate match, and a branded version is a bonus rather than a requirement.

Keep a running BOM file per project, and one master "wanted" list across projects. The master list is what makes batching possible later.

Choose generic where it does not matter

A great deal of maker hardware comes from the same few chips on boards of varying polish. A generic ESP32 dev board and a premium one run the same silicon and the same firmware. The premium board may give you better antenna layout, cleaner power regulation, a documented pinout, a reset button that behaves, or a seller who answers questions. The generic board gives you a working microcontroller for less.

Whether that difference matters depends on the project. A sensor node on a shelf, powered from USB, reporting every few minutes, will not care. A battery device that has to sleep at microamps will, because regulators and pull-up resistors on cheap boards often waste current in deep sleep. If low power is the goal, read the listing, look at the schematic if one exists, and consider paying for a board that documents its sleep current.

Generic is fine for these in most projects:

• Dev boards for ESP32, ESP8266, Arduino Nano-style and RP2040 designs, when you are prototyping.
• Bare sensor breakouts, such as a BME280, DS18B20 probe, or a PIR module.
• Passives, headers, jumper wires, breadboards, tactile switches, LEDs.
• USB-serial adapters. A CH340 adapter and a CP2102 adapter both flash an ESP32; the main difference is driver support on your operating system.
• Small displays such as 0.96 inch OLED modules, as long as you check the driver chip and the I2C address.

"Generic" does not mean "unchecked". The chip family and the form factor still decide whether it works. A BMP280 looks almost identical to a BME280 but has no humidity sensor. A different board with a similar name can have different pin positions. Read the chip markings in the listing photos, and see choosing the right variant for how the options on a listing change what arrives.

Pay more where failure is expensive

Cheap is a property of the part, not of the project. A few categories are worth paying for, either because a failure destroys other parts or because it can hurt someone.

Mains power. Anything that connects to household voltage should be a finished, certified product: a plug-in adapter, an enclosed AC-DC module, a relay board built to be used with mains. Look for the CE marking and a brand you can identify, and keep the mains side enclosed. A cheap unbranded wall adapter may meet no standard at all, and the saving is not worth it. If you are not experienced with mains wiring, buy a ready-made smart plug or an enclosed supply and keep your own work at low voltage.

Chargers and power supplies. A flaky 5 V supply produces the kind of problem that wastes a weekend: random resets, corrupted flash writes, sensors that read slightly off. A stable USB supply from a known maker costs little compared with the hours lost. Test generic regulator modules under load with a multimeter before trusting them with a board you care about.

Lithium cells. Buy cells from a seller who states the capacity and a recognisable cell maker. Very large claimed capacities on tiny cells are a warning sign, and many cheap listings overstate them. Lithium cells also count as dangerous goods for air freight, so many shipping lines refuse them or charge more, and that is worth checking before you add one to an order. In many cases the cheapest sensible plan is to buy the cell locally and the rest of the project overseas.

Charging and protection circuits. A TP4056 module charges a single lithium cell and is cheap and popular. Many versions have no protection against over-discharge or short circuit, while others add a protection chip on the same board. Which one you receive depends on the listing and variant, so check the photos and the description, and do not assume. If the cell goes into a device you leave unattended, use a protected cell or a module with protection.

Why shipping dominates small parts

The unit price of a resistor, a header or a sensor module is so low that everything else matters more. Shipping, agent fees and import charges are largely per parcel or per item, not per euro of goods, so a cheap part can end up costing several times its sticker price once it arrives.

Some of this is recent. The EU's €150 customs duty exemption ended on 1 July 2026, and a temporary €3 customs duty per item, counted per tariff classification, has applied since then. A €2 EU handling fee per item is scheduled from 1 November 2026, and is not yet in force at the time of writing. VAT has applied to low-value imports since 2021, and the IOSS scheme can collect it at checkout on consignments up to €150. The European Commission's page on the €3 duty on low-value e-commerce consignments is the place to check the current rules, and what landed cost really includes breaks down every layer.

Declare what you buy honestly and plan around the charges. Do not split parcels to stay under a threshold or declare less than the true value; that is not saving money, it is a customs problem.

Buy small cheap parts in packs

Because the per-parcel and per-line costs are fixed, the marginal cost of extra copies of a cheap part is tiny. If a resistor kit, a bag of 100 pin headers or a pack of ten tactile switches costs a little more than one, buy the pack. You will use them across the next five projects.

This stops being true for expensive or untested parts: do not buy ten of an unproven display on the strength of a listing.

Batch across projects

The most effective single saving is also the dullest. Keep a shared wanted list, and place one larger order every few weeks rather than a small order every time you think of something.

One order means one international shipment and one set of agent handling. It also lets you share a parcel's fixed costs across everything in it. Illustrative arithmetic, with made-up round numbers: if a parcel had a fixed cost of 10 euros and you bought one part in it, that part carries 10 euros. If you bought twenty parts in the same parcel, each carries 50 cents. The real figures depend on the route and the weight, and the per-item customs charges described above do not shrink this way, but the principle holds for most of the other costs.

The catch is time. Your parts sit in an agent's warehouse until the last item from the last seller arrives, and free storage periods are limited. How to buy from 1688 explains the flow. If you are working to a deadline, the faster local shop may genuinely be the right choice, and there is nothing wrong with that. Resellers who hold stock nearby give you speed, easy returns and someone to ask when it does not work; stop paying the middleman looks at when that is worth the premium.

Reuse, salvage and avoid kit bloat

The cheapest part is the one you already own.

Old electronics yield USB cables, switches, connectors, motors, fans, buttons and speakers. Salvaged parts are not always reliable, so they suit prototypes and non-critical roles. Do not salvage lithium cells from damaged equipment, and keep clear of the insides of mains-powered supplies, where capacitors can hold a charge after unplugging.

Be wary of starter kits. A kit that includes dozens of sensors, a bag of jumper wires and an assortment of components is good value only if you will use a large share of it. Many people use five parts and shelve the rest. A kit can make sense for learning from scratch. If you already know what you want to build, a BOM of exactly those parts costs less and leaves no clutter.

Finally, prototype on one unit before buying ten. Order a single board, a single sensor, and make the project work on the bench. Then order the quantity for the real build. Buying in bulk before you know the part works is how a cheap project becomes an expensive one, because a wrong variant multiplied by ten is a large mistake.

Worked example: an ESP32 sensor node

The project: a small node that reads temperature, humidity and pressure and sends the values over Wi-Fi. It runs from USB power, sits on a shelf, and reports every few minutes. The table lists the BOM with what matters in each line. Prices are deliberately left out, because they change and they depend on the listing.

Read down the second column and the shape of the method appears. The parts with a clear functional requirement (BME280 versus BMP280, data cable versus charge-only cable) are the ones to check carefully in the listing. The parts where only the function matters (headers, wire, box) are where you buy cheap and in bulk. The one part where the answer is "buy a known one" is the power supply, and it is also the one least interesting to shop for overseas, since a good local adapter is easy to find.

Note what the example leaves out: no lithium cell, no mains, no charger. Adding battery power would change the BOM substantially, with a protected cell, a charger with protection, a low-quiescent regulator and the shipping rules for batteries. That is where the cheap generic approach starts to lose to a more careful one.

The order itself is then mechanical. One ESP32 board and one BME280 to prove the design, a pack of headers and wires shared with other projects, and a decent USB supply from a local shop. Once the prototype works, add the second and third node to the next batch. If an item comes through a marketplace and an agent, confirm the variant before you pay, and again when the agent's photos arrive.

FAQ

What is the cheapest way to start with Arduino or ESP32 projects?

Buy one generic board, one or two sensors, a data-capable USB cable and a breadboard, and learn on those. Skip the large kit unless you know you will use most of it. A BOM of exactly what your first project needs is usually cheaper and leaves nothing unused.

Are cheap Chinese dev boards good enough?

For prototyping and non-critical projects, usually yes. They use the same chips as pricier boards. What you give up is documentation, layout care, support and sometimes low-power behaviour. Check the exact chip variant and form factor in the listing, and treat any match as a lead to verify rather than a guarantee.

Which parts should I never buy cheap?

Anything on mains voltage, chargers and power supplies you depend on, and lithium cells. These are the parts where a failure can damage other hardware or cause harm. Buy certified, identifiable products, and read the shipping rules before ordering cells from overseas.

Is it cheaper to order many small parcels or one big one?

One bigger parcel is usually cheaper per item, because shipping and agent costs are largely fixed per parcel. The trade-off is waiting for everything to arrive and watching storage limits. Do not split an order or understate its value to avoid duty or VAT; declare it accurately and compare the real quote.

Plan your next project

Browse the catalogue for the parts on your BOM, compare the matched listings and variants, and add what you want to your haul, which shows the goods subtotal. Freight, agent fees, international shipping and import charges come on top, so check them before you pay. How it works explains the matching, which is automatic and can be wrong, so always read the listing and variant before ordering. Some Superbuy links on PartLark are affiliate links; the catalogue is the same whichever agent you use.