$500 each
During the mining boom, everything that could perform the necessary calculations was used. In particular, we saw how partially defective processors from the PlayStation 5 were adapted for mining. Now anyone can buy such a solution.
On eBay, offers have appeared for the sale of ASRock BC-250 boards, which are based on the APU from the PS5. Such processors have some defects that prevent them from being used in consoles, but there are no details about which units do not work there. Given the specifics of mining, probably CPU blocks.
At one time, such boards were not sold separately, but as part of a ready-made farm of 12 boards, for which the performance was claimed to be 610 MH/s. On eBay you can now buy such boards separately. True, at a price of $500 apiece, which can hardly be called a good deal.