I went to Harbor Freight today. They have an air compressor good to 150 PSI that is powered by the vehicles battery. It's normally $69.99 on sale for $49.99. Also, you can print a coupon for $10 off. All in all, I just got onboard air for $40.

Here is the link:
http://www.harborfreight.com/cpi/cta...emnumber=93186