Fish tank anyone?

Last year, I purchased a new fish tank for the classroom. We have since kept a few fish as our classroom pets. These last two weeks we have had a frog and a few minnows in it. Somehow, this week, it was broken! A new tank is quite costly, yet housing and caring for a few fish is a valuable exercise, so I would still like to have an aquarium. If you have one at home, that you are no longer using, and you wouldn't mind giving/lending/selling, please let me know. If you find one at a yard/garage sale that is reasonably priced, I would happily reimburse you. Space is somewhat limited, so it must b about 18 inches long. Thanks for your consideration.