Come to think of it, they are pretty good at getting your heart rate up. Have you thought about paying someone for a few private lessons and then just doing it by yourself or with a friend. That way if you know someone with a pool you'll be able to save some money and if not you can still go to your local pool when it's convienient and dont have to worry about class times.

BTW the ladies in my classes just do the low impact version if the normal way is too much for them.