If you got a few extra dollars you can take it to an alteration shop. Shouldn't cost too much and you can pick what type of zippers you want (i.e. metal or plastic) other wise the only thing I can think of is go to the wal-mart craft section or a craft store and get the supplies to sew on new zippers. The ppl in the craft section/store can tell you what you need and how to do it.
shit with a reciept you can return anything from nearly anywhere. and if no recoiept you can retrn to lots of other stores too:walmart, K-mart, places like that.
rip out the old zipper, find a new one (like cut one off a trashed backpack or something that is about the same size) and with the new zipper zipped together, sew it onto both sides and try to keep it sturdy (ie, tight stitches). cut it down to size and you should have a pretty good zipper, kinda hard to mess up.