see my post above for some of the info, but here's some more.

the common sizes of co2 are sold by weight - #5, 10 & 20 - although i'm not sure of the tank pressure, it's probably around 2,000 or so. you can get two types of regulators, i had a 150 psi fixed regulator it had no adjustment or gauge, or you can get an adjustable that reads cylinder pressure and output pressure. the adjustable regulator will flow faster and is suitable for running air tools like an impact, the fixed regulator is really only good for airing things up like tires or beach floaties.

here is a chart from powertank's site - it should help you get an idea of the volume necessary. as i said before each tank fill will cost $15-20