Something to consider - that rockhopper listed for $65 but made in 91 is way different than any Rockhopper being sold today. Those old Rocks were I think fully rigid, steel framed bikes. Not a bad buy for $65 but the bike is not ungradeable. What you see is what you get and what condition are the wheels, brakes and shifters. Can components be purchased to replace those parts if repairs are needed? If you just want a kick around, computer bike, this is probably a good buy provided its in good working order.

It's hard to judge the price of a bike, especially used as wear is a big part of the value. If the bike ws bought new, never or hardly ridden, kept tuned and clean and never just sat out in the garage, then value is still going to be at least 75% less than the original price. And the less expensive the bike was in the first place, the more it depreciates.

A good quality bike depreciates less. For instance - take a 2004 Litespeed Solano. The bike sold new for $3000. Note this is a Ti bike with full Ultegra. The next year, new 2004 were selling for about $2100 and some for even $1900. If used, the bike was be worth around $1400 - 1500 even in good shape. I would say this year the bike's price will drop significantly - if new down to $1600 and if used around $1200.

There is nothing wrong with buying a used bike and I have friends that have gotten some absolute steals by checking out garage sales. A good friend purchased a Colnago C40 with full Campy Record and ZIPP 404 wheels for $2,000. The bike was just sitting in some guys garage collecting dust. The wheels alone are worth almost that much. Just keep looking. SOme treasure will turn up.