Wal-mart has small critter keepers for 6 bucks, but I understand the whole saving for a car thing
I am as well.
And no I wouldn't treat the community, there is a chance you could kill your snail since they are sensitive to things like that.
For the time being just wait it out and see if it get's worse. How old is he or how long have you had him? He looks pretty young to me.
EDIT: oh I forgot! I also use regular Plastic ware for QT containers. Like the ones you store food in, I buy a new pack at Wal-Mart, generally 2-3 bucks for a pack of three. Find out how much it contains, it should say on the package and then you can convert to gallons online to see how much salt you should be mixing up to treat him healthily