Assuming you know what size you are looking for, check bikesdirect.com and bikeisland.com - just make sure to re-assemble everything prior to riding. If you go this route it may be prudent to set aside a few extra bucks to have a local shop tighten up the wheels as well.

$200 isn't much of a budget, but it can be done. Keep it single speed and you won't have a drivetrain to keep clean.