Here's a small US-based PCB board and assembly facility in the US, in Hesperia, California.[1] Looks like it might have 20 to 30 employees from the building picture. This is probably about as small as a viable business of this type gets. It doesn't have to be done in a huge plant like JLCPCB in Shenzhen.
Here's a company in India, Invariance, which makes low-cost semi-automatic machines to do exactly the same operations 39c3 is doing.[2] They have three machines - a solder paste spreader, a pick and place machine, and a mini tunnel reflow oven. They make all three machines. These machines intended for small companies who want to assemble their own boards in house. The solder paste spreader is just automated enough to do a consistent job, with pressure and timing controlled. The pick and place machine uses their own feeder design which runs off strips of component tape. The tunnel oven is small, only about a meter long.
That's close to a viable minimum production solution.
