I have a PCB that I designed that has around 40 components (mostly resistors and capacitors) on a board that is 40 mm by 80 mm. I have the BOM, pick and place file, and gerber file. If I provide the parts and request a lenient lead time. How much should it cost a unit?
I reached out to an assembly company who said it would cost $800 for a single unit. That seems completely insane. Shouldn't it be cheaper?
A lot of PCBA cost is in NRE (non-recurring engineering). They have to set up equipment on the line whether the ordered quantity is 1 or 10k. Depending on board complexity and component choices, they might forego certain steps or equipment on the line and hand-assemble or selective solder, etc.
Also consider that the board house might have to dedicate equipment for a block of time to your single board run, but it could have been running some other larger job, earning them more money. They are going to adjust your price to make it worth their while.
As you order larger quantities, the unit cost will decrease significantly as NRE is spread among your boards.
If you are working with a quality board house, $800 for full PCBA sounds about right. Shop around, but remember: you get what you pay for.
If you PCB is "standard", ie 1 or 2 layers, no ball grid array components, no very thin traces or clearances, rectangular shape, ... and if a "prototyping" quality is enough for you, then you have plenty of PCB assembly companies that offer very low prices (<50$ exclusing the cost of components). They are often based in china, and simply do several "standard" prototypes (for different clients) at once on the same PCB, and cut it afterwards.
If you don't require high reliability, nor ultra fast assembly, then it might be an interesting solution.
As soon as you start to have some specific requirements on the PCB itself or assembly (ie more than 2 layers, ball grid array, sizes bigger than usually 100*100mm, ...) prices increase, but often remain in the 50-200$ range.
You also get some similar prototyping services in many countries, which is a bit faster, but more expensive.
On the other hand, if you expect "industrial production" with full testing (X-ray, continuity test, isolation test, functional tests, on circuit programming of microcontolers, ...) for a single unit, then it will be very expansive for a single unit.
If you ask a manufacturer specialized in big series, then you will likely pay use setup costs (making the price very high for a single PCB).
So basically, if you want a single PCB (and don't plan a big series of the same wanting to order it from the same manufacturer), then make sure to choose a manufacturer specialized in prototypes. Then you choose between cheep manufacturing in China (with random quality), or expensive manufacturing locally.
PS : from your question, I would guess that you are not very used to have PCBs manufactured and assembled. So excepted if you are in a hurry (which you don't seem to be) or if you have very special requirements, I would start with a cheep assembly, in order to validate your design. If you have to modify something, you avoid paying twice the high price. If it is fine, then you can decide if the prototype is of good enough quality, or if you want to order a "final" version of better quality (this time, without doubts if the design is correct or not), the prototype the being a spare in case you get any issue with the new one.
