...I'm wondering who decides what is overpriced and what's an acceptable price
I think a lot of it, certainly from opinions on these forums, is price-performance ratio of the product itself and the price increase over the previous generation. There is acceptance that introduction of new technologies increase costs because of R&D investment, and recouping manufacturing costs from substantially bigger dies, but if a chunky price increase isn't reflected in performance and capabilities then it's "overpriced".
So using the RTX cards as an example: yes, R&D from the RTX technologies and producing the physically bigger needs to be recouped, so price will increase, but these new features are a
not even implemented in games yet and b
are woefully underpowered in what little demonstration we've seen. So there is a premium to pay for something you can't even use. Then, the part of the card that you
can use isn't significantly faster than the previous generation. But the price has increased by, what, 50% over the previous generation? The disparity between what you get and how much it costs makes it "overpriced".
Same goes for RX Vega: HBM made no discernible difference to gaming performance but there was a big price premium because it existed, plus they performed worse than the price-equivalent Nvidia card. Too hot, too hungry, too slow made vega "overpriced".