It's absolutely overpriced on eBay.
I've had amazing luck with Facebook marketplace and Craigslist, though not just waiting for listings. I make posts saying I'm buying old computers, and kinda generally sketch out what I'm looking for - nothing specific but things like 'Need PC from late 90s for project' or something.
You will, eventually, get a couple of nibbles here and there and sometimes land a legitimate deal but it does require a lot of time and patience that it didn't require a few years ago when you could just literally go get all the retro computer e-waste you could stuff in your car for $0.