I was in sorta the same situation as you-my Grandpa has a compresser, but it was impractical to have to borrow it everytime I wanted to airbrush something. I went to Wal Mart, and got a 7 gallon air tank for $20.00. I bought the various airbrush accesories (hose, regulator, moisture trap, etc>) and hooked it up to the air tank. When I run out of air, I can simply drive over to my Grandpa'a, and refill it.
HTH Chuck