I looked when I was shopping. I was pretty much only looking at Quincys, IRs, and Craftsmans. and for the most part, a similar Quincy compressor to the one I got would have been in the $500 range.
Yeah - but the used compressor market is a different beast. That just indicates how well a product keeps it's value. People are willing to pay more even for a used Quincy because they know they can do an annual service on it and have basically new machine. I doubt you could even get any significant parts for the 20 year old Craftsman - their business model doesn't require supporting things that far out.
Buy a 20 year old Quincy, and in anther 20 years when it's 40 years old you'll still be able to get service parts for it. I just ordered parts for a 1965 QR-370 that's going in our rental fleet after being owned by a local parks department since the early 80's. It was making 60 CFM @ 125 psi when I tore it down .