>Prototyping requires a back and forth costing many thousands of dollars.
This is a problem that is being rapidly solved in the OSHW community, with low cost PCB prototyping services such as OSH Park and similar. Something of the complexity of a laptop motherboard may still be in the thousands of dollars range, but a large variety of hardware is now incredibly affordable.
Even something like a low-cost phone would fall under this. Unless you're making a simple control board for a physical process, OSH Park won't cut it. And of course RMS is talking about computing. Anything at the general computer level is probably not going to work out unless it's really tiny.
This is a problem that is being rapidly solved in the OSHW community, with low cost PCB prototyping services such as OSH Park and similar. Something of the complexity of a laptop motherboard may still be in the thousands of dollars range, but a large variety of hardware is now incredibly affordable.