I would recommend a Speciallized Rockhopper. They are usually in that price range, and they are a pretty good bike. My reason for this recommendation is that you have a more broad variety of riding styles to chose from. If XC is your thing, the Rockhopper is reliable and basic...no extremely difficult parts to work on. But if FR is your thing (like me) the Rockhopper also has a pretty strong frame. I have done some intense urban and parkriding on a Rockhopper (15" frame) and never damaged anything on the bike. So I guess my point is that by starting out on a Rockhopper or similar bike, you will have the ability to see where riding can take you, and what your style is.