Used prices vary a lot based on where you are. Your best bet is to just look around until you find a listing for a good GPU that doesnt look sketchy. Used GPUs, especially around the shortage (which appears to be ending), can be very risky.
You never know how it was treated. It could be broken, fake, or used so heavily, like mining, it doesnt perform well anymore, though that does take a long time. If you can buy a used GPU with a guarantee, and/or the ability to return for a full refund, then it should be fine. If something goes wrong on a GPU without any warranty, then you are out whatever it cost you.Why is it risky to buy used GPU?