Tylar, that is a loaded question!
One place to start is MusicCity's
website, just scroll down past his amazing collection of aircraft models and read up on types of airbrushes, air sources, and other great tips. Wouldn't hurt to bookmark it, as he has lots of information. That will hopefully narrow down your search before your head to
www.dixieart.com or
www.bearair.com to look for your first airbrush.
I don't know what end result your looking for, or what you model
A Paasche H or Badger 200 single action might be a good place to start and could be had for $30-40. A good double action like the Paasche V or Badger 150 will just about double that. Iwata are a pretty good airbrush too, "some" people around here swear by them. They tend to be a little more money, but the Revolution series is around the $65 mark.
It's the compressor that usually breaks the budget. Depending on your situation you might be able to get away with a garage type compressor. Caution: They are LOUD! I would suggest getting one with at least a 3 gallon tank. You'll need to add a better regulator to adjust the pressure, most garage compressor regulators aren't quite fine enough for airbrush spraying. You want one that allows adjustment between 10-25 psi. Also check out Harbor Freight for
airbrush compressors, I've heard good things about that. A "really" good airbrush compressor can go upwards of $200.
Also check out the Airbrush forums, lots and lots of information there.