your budget is a bit difficult to work with if your are looking for a camera and underwater casing to go scuba diving with.. $600 and up for a decent set, goes up to 40m deep usually..
The price range for waterproof camera like olymps mju tough series is also like $400-$600 and u..so far the deepest I,ve seen is 15m.. not for scuba diving, only snorkeling max..more common is 10m..
If u are looking for a camera that does shots for say water sports, maybe even in the pool or light snorkeling, <5m, I would recommend getting a good point and shoot at $400, leaving $50 for soft cases like dicapac..
Hope it helps.. if u can raise ur budget slightly, I think I saw someone selling 2nd hand s95 with underwater casing.. can check it out..
Edit: oops, I read as $450 was ur budget.. haha.. since u have a budget of 900, I would suggest s95 combi for scuba diving.. if u're just starting diving, don't left the frustration with dslr underwater take the fun out of diving.. not yet anyway..