I think that you can get some fairly cheap waterproof cameras, and even some disposable ones.
At the end of the day, it will depend on the clarity of the water as to how good your photos will be - we used ours in the pool to take photos of the kids and they turned out great as the water was really clear and they spend more time underwater than on top!! - My OH did find it quite difficult to see whata he was photographing though as the sun was shining on the screen and he was holding his breath underwater and had goggles on.
What i did find was that I wasn't worried about taking it on the beach as it is equally sand proof as water proof, so all in all it is pretty robust and is useful for all occasions - only disadvantage is that you cant get optical zoom only digital.
I read up a few articles when I was buying mine last year, and some of the disposables got a reasonable write up - in virtuallly everything I read, the waterproof cases were said to be not that effective - the seal seemed to be prone to leakage after using a few times - might have improved by now though. If you are going snorkelling with a guide, I am pretty sure that they will take photos of you that you can buy.