I would recommend a one time purchase - the Aztec A470.
My experience has been that this is a spectacular tool that is very easy to learn how to use. It comes in a wooden box, with multiple nozzels which can be used for a variety of model applications (although I have only found it necessary to use two).
It also comes with a brief (20 minute) VHS tape which explains how to use and clean it.
1. The brush is easy to clean (spend the bucks to get the cleaning station as well) which is often the nightmare problem with airbrushes. This means you can change colors rapidly.
2. The brush is reliable - I have had no failures
3. The brush has simply fabulous support by 800 number from testors
4. The brush will work just fine with testor's paint right out of the bottle
5. The brush can be used in two mode - single action or double action. As a beginner you will probably start with single action, but it is surprisingly easy to move to double action
6. I had used a single action badger for about 20 years before moving to this brush, and found it splendid. My son, who has never used an airbrush before started with the Aztec and also loves it.
Rember, you will have to get a good compressor as well.
Best regards
Jim Fink