Whatever you do, don't get something that ever came from Target, Sears, Wal-Mart, any place like that. They're complete POSs, not really even considered real bikes by anyone who's even semi-serious about cycling. Bikes like that aren't fun. They're heavy and hard to pedal.
I second the suggestion that you look on the used market. Bicycly resale is pretty low after a couple years, even if the bike was hardly ridden. You can probably get something for your (US) price range that's not very used, and only a couple years old, like a Trek 4xxx, or a Specialized Hard Rock, etc., that was selling around $400 (US) new. It might even have a couple worthwhile accessories or upgrades thrown in!
Good luck, have fun riding, and remember, lights at night!