Best thing is go find a REAL Local Bike Store (LBS) that deals in both used and new. This will be a shop frequented by bike enthusiasts, probably will be home base for a Club. The staff will greet you with grease on their hands. See what they offer, test ride them. Stay far away from Kmart, Target, WalMart, big sports discount warehouses, etc.

In bikes, you really do get what you pay for, so you usually can't get a great bike for a low price... and you can certainly get cheated and pay lots of money for a bad bike.