Honestly, for a bike, I think a 2-3 hour drive would be worth it as long as the shop has a decent reputation. They will be able to answer a lot of questions for you and help you figure out sizing, and in all likelihood will help you figure out what you are/should be looking for. If they carry used bikes, as previously mentioned, they may have something in your price range. Unfortunately, there isn't a frame size that fits everyone that is 5'6", there are many variables, including the type of bike. As a former bike mechanic, who specialized in fit, I could never in good conscious recommend a size online.

If you must buy from somewhere other than a bike shop, I'll suggest bikesdirect.com, as their bikes tend to be much better quality than the Thruster, but still affordable. You won't find anything for $200, but if you save up a bit more I think you'll find it worth it. They have a nice cross bike single speed as well as a fixed gear road bike. I've ridden both and like them both.