Bike Forums - used bike resources

A friend of mine is looking to get a new bike but is unsure what to get and where to look for a good deal (target price-approx $300). He's unsure if he's really interested and doesn't want to invest too much. I recommended a good, used hard-tail mountain bike as he won't be doing anything hard core initially, but wants a versatile, durable ride for road and light trail use. I believe in paying for quality, but also understand his financial constraints, and think that he'll get more bang for the buck in the used market. He actually felt compelled to look at Target for Huffys. He's also looked at some '02 clearance bikes at Performance but is a little put off by the $400-$500 (and up) price tags. I know there's too many variables to cover here, but what can you recommend in terms of shopping for used bikes? He's a little dismayed at the prices he's seen on Ebay, internet searches haven't revealed much, and an lbs bulletin board is pretty hit or miss in my opinion. Bear in mind that he doesn't want to buy anything "sight unseen". I also recommended checking out a police auction as well. We both live in the DC-Metro area. Thanks in advance for any help.