My first "grown up" bike was a Magna mountain bike from Target. Put a lot of miles on it before it was stolen. My next bike (some ten years later) came from Sports Authority and was near your price range. We shared thousands of happy miles together before I realized she was too small for me. Also, I had been reading TE long enough to start coveting a road bike--a better road bike. If you stick around long enough, you'll eventually succumb to bike envy and an upgrade is likely to follow...