Nowadays you don't have the option of buying them anywhere else than a gun shop....precharged air rifles although the valve is different use the same 7 oz bottles that are used in paintball and they charge a small fortune for them so the same is probably true of the 12 grams now. I last paid many years ago 35p each for them up to as much as 50p when playing tournaments, some things are only cheaper in relative terms as what you could get for 50p ten years ago won't get you much now..though your wages are higher now so they are probably the same price now.