Thanks everyone for the info! I had actually thought of trying to adapt my dad's old CPAP machine into an airbrush compressor, since it's so quiet... crazy? maybe ...
As for the CO2 option, I'm really liking that direction. I'm seeing small tanks on craigslist pretty cheap. Can you tell me more about what I'd need to do to make that work? Do I need a regulator? Where do you refill them?
Sorry - I have ZERO experience with an airbrush, but have done about every other form of art, and know if I get the air source right, I'll be an airbrush addict!