Well it depends, are you getting the really big striped ramshorns (which is a type of flat apple snail) or the tiny pond variety that come in red or brown? If it's the latter my LFS gives me those for free, but the first is usually 1-2 dollars.
Also, do you want to breed them or do you just want to look at them? I think you could easily stick them in a 10 gallon even if you were breeding them. Feed them zucchini often and you should have a million in no time. Make sure your pH is 7.0 or higher and you shouldn't have to do much to take care of them, they're easy.
If you are putting them in with other fish, even 24 of the small ones is not that heavy a load imo. If it's the large ones you should get them a tank.