I'm probably one of the few willing to buy a SPARC computer that is completely free, even at the likely 500% markup or more required to build it.
But I also imagine it would be impossible to build due to how few of us even care.
You would need chips, which are pretty much not being manufactured anymore. Good luck buying fab time as TSMC, and having enough volume to justify it. You also need a design, thankfully the SPARC chips have open designs, but they are still really old for old fab tech. Good luck getting the engineers to update it.
You need mainboards, assembled somewhere (expensive) and fabbed (again, expensive). You could invent your own or reuse a published ancient print if any exist.
You would need open designed DRAM, and good luck trying to support modern iterations like ddr3 or 4 on old SPARC boards. I'm not aware of any DRAM being sold with open blueprints, but also have not looked much into it.
You would need open storage devices. No SSD or HDD qualifies today, since they all have proprietary microcode controllers. No open designs or firmware to be found there.
You would need a graphics accelerator. While there are some purely free software GPU drivers (Broadcom for the Raspi) none of the designs are open. Again, good luck.
All combined the cost of just getting these five core components in a firmware free / open design state is insane. It would be on the order of tens or hundreds or probably a billion or more USD just to get a few thousand units. And at those kinds of costs (lets say we are optimistic and sell 10,000 fully open computers) and say it cost only 100M to build them, they would be $10,000 each for what is probably as powerful as something proprietary you could pick up today for $50-100.
One day I'm absolutely certain there will be a sustainable market for such a computer, because with proprietary hardware and software you are guaranteed to eventually be screwed over. Its only a matter of how deep in the rabbit hole you want to get before you wake up and realize how bad an idea it is. Eventually, I am certain all hardware and software design will be open, its just a matter of how long we want to slow progress and risk our individual prosperity on proprietary tools until enough wake up to the problem.