Underwater Photography is generally an expensive hobby, however EWA-Marine are trying to help the more casual photographer getting their kit under the waves.
EWA-Marine have a PVC bag that allows you to take your SLR Camera underwater for under 100 USD.
It looks like a reasonably priced, simple product to get people clicking underwater. IT should also cater for most recreational diver as they are rated down to 30m.
You can read more about this bag on the EWA-Marine website