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Check out http://www.tcpglobal.com/airbrushdepot/. They have an AirBrush-Depot Tank Compressor that has worked well for me for $150, which is a good price for a tank compressor. You can get just the compressor for $110 but, if your budget allows, the air tank will give you much smoother results than running straight from a compressor.
I suggest buying an air compressor from Sears (on sale if you hit it right). I first had a puny little Badger that was bought at a ridiculously high price and was only a diaphragm pump. You can buy a piston type compressor with tank/accessories for around $130 or so and all you need to add is a moisture/oil trap. Don't waste your money on all these little hobby compressors when you can have one that will do more quicker, better, and cheaper.
I bought a 1 gallon compressor from Lowe's for $70. It also came with a crown stapler/brad nailer. It does a fine job but 1 gallon won't let you spray continuously for long periods of time. But, for $70 I have no complaints. Figure another $30 for an air dryer, regulator, and a couple of fittings.
I bought a Campbell-hausfeld compressor with a three gallon tank and a regulator for 75.00 at Lowes a few year back. After it pumps up (noisily) I can spray for 1/2 hr with no noise. Depends if anyone around you objects to an occasional noisy run up.
Refrigerator engine (used), add an air filter(car gasoline filter) in the intake and a oil filter in the pipe to the airbrush, works terrific, didnt make noise and it cost me just $25
Just to chime in - I used to be an avid scuba diver (still do, just not as much). My airbrush runs right off one of my steel 90 tanks. Not as dry as CO2 but it's nice and quiet and lasts a long time. I get pretty good results from it.
I just recently purchased 2 fittings to hook up my wife's nebulizer compressor for the airbrush. It has variable pressure and seems to work great. I may need to add a moisture trap, unless I only use water-based paints.
Check out the thread: Air Brushing and weathering using an air compressor?
I use two compressors: my shop compressor (a 5.5 hp / 30 gallon Ingersol-Rand) piped into the hobby workroom, and a portable Craftsman 1 hp / 6 gal. I got on sale for $85.
Lowes has a small 1 gal compressor with a brad nailer for $79. It was on sale on Black Friday for $49. If you're not in a great hurry, I wouldn't be surprised if the price drops again before Christmas. They didn't sell well - I still have two pallets of them in top stock.