Here is another usefull idea:
Get a high wattage power inverter. We're talking one on the order of 600+ watts. Yes, these cost a few bucks, but for what you get, its worth it.
Next, buy a (very) small air compressor that will run from it. How do you know if it will run off of the power inverter? Look on the back and find how many amps it requires to run, multiply this by 115v and you have how many watts it requires.
example: 115 volts * 5 amps = 575 watts (or more).
This way you have double utility, an inverter this size will easily operate drills, grinders, and some saws. Also, you get a quality large (compared to most on-board systems) capacity aircompressor capeable of running impact wrenches (if only for a few bolts at a time).
the total cost of this setup is going to be 200 to 300 dollars, making comprable to many systems I have seen.