I have been using cheep housings for years,Currently I am using a 4 year old Sony P150 with housing.
When looking at a camera you have a few things to consider
1. Use - If it is just an underwater camera, how much use are you going to get from it.
2. Space - if you are travelling abroad, size and weight become an issue.
3. Cost - do you want to take a Really expensive camera underwater, if the case does flood, it could be a big loss.
4. Light - You can have the greatest camera in the world, but you need a good flash - if you have an option get an external.
5. Speed - you don't want your camera to stop and think for a few seconds after you press the shutter - most things you shoot will me moving, and you may well be as well - so it has to be quick to get the image you want.
6. Depth - if you don't ever dive below 20m, do you need a camera that will go to 60?
Using the internal flash on my sony has had some good results, but the further you get, the more blue it becomes. My case is rated to go to 40m, though it's ok to 50m.
http://www.wallbridge-art.co.uk/bryan/photography/diving/
Should show you some expamples. I am looking to upgrade my compact camera soon (I have a nikon D200, that I won't be taking diving, to big and to expensive)and will be making sure there is a cheep housing for whatever I get. Sony are pretty good for housings, don't really know about anyone else right now.
Bryan