Earlier quoted context omitted.
Prices for used GPUs are also inflated, though I think they have started to come down a bit. Once Ethereum moves to proof-of-stake (early 2022?) the market will probably get flooded with used GPUs.
I don't think proof-of-stake will actually work. Not because of any technical reasons, but because 95% of the people involved in crypto just see it as a free money printing machine. Once their hardware is no longer useful for mining, they will just move to some other proof-of-work crypto.
If proof-of-stake works out, particularly as a currency people can actually use, then maybe nobody wants to buy Bitcoin anymore and the whole thing dries up as only speculators are left.