For example JLPCB https://cart.jlcpcb.com/quote?fromDemo=yes You first order is $10 including parts and assembly for 5 boards with 4 day turn (1 for pcb fab, 3 for assembly). Typically the boards I have done (comparable to complexity to an arduino) are about $20 for 5 copies including fab and assembly. They also have a free cad tool called easyEDA https://easyeda.com/ but I would really recommend kicad. It takes like 5 clicks to go from layout in kicad to boards at jlpcb https://support.jlcpcb.com/article/44-how-to-export-kicad-pc...
PCBway has a lot more capability, but is a bit more expensive https://www.pcbway.com/orderonline.aspx
I used ExpressPCB for a small project back when all these tools were very expensive and there weren't any good free ones. I found it very easy to use.
If I did not have professional tools available today, I would use KiCAD or TinyCAD + FreePCB and pick my board vendor independently.
Things I care about: * Board fabrication AND final assembly * Quick turnaround time * Small minimum order size (preferably 1) * Help choosing components
Things I DON'T care about: * Getting the absolute cheapest price * Being locked into a vendor for a particular project * Tight tolerances on things like thermal management or AC signal integrity.
I just want to have a custom board for my PIC-based project, or my one-off guitar pedal circuit.
I haven't tried this service, but I will. If anyone knows of other similar services, I would love to hear about them as well.