the best and cheapest way is to get a couple scuba tanks. the tanks will run you about 150-180 a piece new and you'll prolly want 2. the scube fill will be about 40-55 bucks. you can get the tanks at a dive shop (you may need to get someone certified to buy it or explain that they will be used for PB) and the fill station at pbgear.com
or your local pro shop might have one. then a dive shop can fill the scuba tanks
or go to a welding supply company and try to buy a used tank but you'll need to be 18 to buy a full size tank and then you have to buy a 400 fill station! and the welding supply company should be able to refill it.