[ahimel]

If you or your housemates are already gamers, consider Dance Dance Revolution. It has an exercise mode where, instead of accuracy, it tracks calories burnt. Slower songs allow for warm-up, and the better you are, the more calories you burn.

If you already have a PS2, game+pad will run under $100. If you don't have a console, or know where you can get/borrow one cheaply, it's probably not worth the effort.