They already are. You can go and buy an AMD RX 580 with 8GB VRAM for 250€ in Germany. The RX 580, 570, 470, and 470 were the most efficient cards for mining Ethereum in terms of power usage, hashrate, and cost.
1080Tis can be found under 400 in NYC
I'm also curious what happened to all that custom FPGA and ASIC hardware that miners were using for a while.
Surely it's sitting unused somewhere, right?
There weren't many FPGAs AFAIK. I wish there were and the cheap big used FPGA boards are all over the market though.