[mbsmith]

Kodak and Fuji make nice disposable underwater cameras for about $15 test your ideas with one of these before you get into a Nikonos system, while they are great cameras I would not recommend them for someone that is just going to take a couple of hundred photos in shallow water. They also make budget 35mm cameras with flash in waterproof cases that can be reloaded at reasonable prices.

I have a Sea Life Sportdiver (rated to 50m) that I let the kids use in the pool that is very affordable (basically just a p&s with a tough underwater case) and takes reasonably good photos. They make several models with accessory shoe that might also be an option if you don't go the Nikonos direction.