hey, paintball tanks range from $20-$60 usually. I like having the two 9oz's because then I always have a backup, and never run out in mid-kill. Oh man that would suck for the rats. And as for how many times you can use it? Get this, I got those 2 filled around the time I first posted this thread, and I just got them refilled for the first time tonight!I've probly killed between 100-200 rats since then.