...and what happens if I got cheap on a air compressor?
Also what do you mean by tank? do you mean the canister air brush?
Cheap doesn't matter. I paid $50 for my pancake air compressor and it's perfect.
Compressor:
What's meant by a tank is that it can store pressurized air, rather than having to constantly pump. Charge the compressor up to, say, 100psi, turn it off. Set regulator to, oh, 20psi, and (with an airbrush) you can paint for quite awhile, depending on the size of the tank.
My Pancake air compressor is a 1 gallon tank, goes to 110psi max, and when I'm airbrushing, it lasts a long time. The damn thing is noisy as hell, but it works great.
NOTE: Be sure to invest in an
pressure regulator and a
moisture trap if the compressor doesn't include them. Regulator because too much pressure splatters the paint, which is bad. Moisture trap because splattering drops of water into nearby wet paint is also bad.
Regulator/Moisture Trap: