I uderstand the arguments for a quality compressor, but I have a 150 gal. comressor for air tools and I would never dream of using it for hobby airbrushing. The best alternative that hasn't been brought up is CO2, and not from the useless hobby cans.
I became a convert to CO2 for airbrushing about 6 years ago when my Paasche compressor died. I slipped a Pepsi truck driver $20 and got a fully charged 20# CO2 tank with regulator. I found an adapter at a hardware store that allowed me to connect my airbrush directly to the regulator. A single charge lasts for YEARS (literally) when painting N scale stuff. Airflow is constant, silent, and moisture-free. I can paint any time day or night without waking the house or the neighbors with compressor noise.
If you go this route, don't "buy" a tank or go anywhere besdies a beverage distributor. CO2 is all they deal with so it is very reasonable. You're essentially "renting" the tank from the distributor and they will either replace the tank when empty or refill the one you have. I just got my tank refilled for less than $20 at another distributor.
It's worth consideration if you're just starting out or searching for a replacement compressor:
]http://www.trainboard.com/railimages/showphoto.php/photo/69735]
