compressed air will work on all guns. i would recomend compressed air because it isnt affected my temperature changes so your pressure is always consistant. tank come in 2 catagorys 3000psi tank and 4500psi tank. 3000psi tanks are usually heavier and made of metal, while the 4500psi tanks are made of carbon fiber and are very light weight. tanks also come in different sizes the most common sizes for 4500psi tanks are 48ci and 68ci, but they can go up too 90ci. the 3000psi tanks can be as small as 13ci and can get as big as 62ci.
right now action village has a 68/45 tank for $100
Worrgames Stratos Preset N2 Tank - 68ci 4500psi at ActionVillage.com : Paintball
and paintball-online has a 70/45 tank for $100
Pure Energy 70ci 4500psi HPA Tank w/ Reactor 2 Regulator
now all you have to do is pick your poison