cheap N2 or HPA,they are the same thing but you will need a 68 square inch 3000 psi if you wanna think about gettign a gun you can walk the trigger with cause I have a B2K and i dont even walk the trigger and i cna use like 1/3 of the air in my 68ci 3000psi in a 30 minute CTF or elimination game...so unless you wnana be an idiot and get a steel tank its gonna cost you more than $100...