[Christ]

I fill my tanks up to 100 PSI at the gas station thingy. Costs me $0.75US to do so, and I can usually fill two 10 gallon tanks.

I own 4 air compressors... they're all at my Father's house, I use my Father in Law's compressor when I need to use air tools.

You can build an air compressor from junkyard parts relatively cheaply, by the way. I'd say around $50 will get you a decent compressor setup, and you can use an old propane tank for a detached holding tank.

I used to re-use those 1lb propane tanks for torches for exactly this purpose, until I bought a refilling setup for them. I'd fill them up to 150PSI, then throw them in the trunk next to a can of fix a flat or Slime.

150 PSI in a small cylinder will fill an average car tire up to 40 PSI before equalizing, IIRC. I'm going to get around to make a few more at some point, because they were actually quite handy for replacing the spare tire in the car.