this has been covered many times on pirate and mud. You can make your own for a LOT cheaper. Old fire extinguishers make great tanks, and valves are 15.00, regulators can be had for 30.00, and it takes about 15.00 ~ 20.00 to fill a 10~15 lb bottle. You can get about 5 fills from 10 psi on 37's.
Personally, I don't think that it's worth the 250~350.00 you would pay a vendor.
Hell, you can lease a tank from linweld for 99.00, buy a regulator, and STILL be a head of the game.