I started with a Iwata-medea Eclipse
Hp Cs
Most of the stuff I have read, is don't
cheap out on your compressor.
Buying a cheap airbrush is clearly a great idea, because you are going to break something. And if by some miracle you don't as pointed out, now you have a airbrush for varnishing and stuff you don't want to muddy up your good brush with.
I have already in a few months time had to replace my nozzle. Which I destroyed, and I clearly have nicked my needle, but it is still working thank god.
So in summary. A cheap compressor will be a poor investment. Where as a cheap airbrush can be a good investment.
Other things you need to factor in.
Are you going to be working in a very well ventilated space? If not you need to look at the cost of a respirator. Or a spray booth. I was having my throat severely irritated until I got my respirator.
Are you going to get really frustrated with the process of thinning your own paints? Now you need to factor buying airbrush paints.
You are going to need a cleaning pot.
http://www.iwata-medea.com/products/accessories/table-top-cleaning-station/
If you are severely limited by money I would consider just start saving over the course of a year. Work on your brushwork in the meantime. Instead of just jumping in to airbrushing.
Patience can also be rewarded, you might decide painting miniatures is no longer interesting to you. Or you could watch for things to come on sale.