I dont know if they still got it, but in a certain big-box store (that is dominating the US retail market), they were selling a Sea-Life underwater camera for around $25. This camera has a yellow body and a silly looking black-plastic crosshairs target scope on top. I don't remember how deep you can go with it, but I am pretty sure it was deeper than just 10 to 15 feet as labeled on the disposible underwater cameras. And this camera uses the regular 35 rolls; so you can open it to change rolls. (But NOT UNDERWATER )
Of course, if you can afford it, I would go for one of the underwater digital cameras. You can take profoundly more photos than with a 35mm film camera (especially if you use a memory card with 2GB or greater). In my situation, I use the Panasonic Lumix FX-01 which has a underwater case sold separately. This underwater case is really expensive but worth it. I could go more than 100 feet underwater with it and have total control of the camera. I think the FX-01 might be obsolete (I don't see it for sale anymore) but I am sure it has a sucessor. I am more than happy with mine.