I'm new to underwater photography too. I just bought a used camera from E-bay for $165. It is a Sea&Sea Motormarine, older model, it came with a strobe and close up lens and all kinds of nice little goodies. (now I just have to figure out how to work it!). This is what I have learned so far:
Look on E-bay!
Check out the Sea Life Reefmaster CL, it runs about $100 new and is good to 100ft. It is a camera with housing, but has options to add strobes, etc. later if you want. It is also fully automatic. A friend of mine has one and it took pretty good pics. at 60-70ft. I've seen a few on E-bay go for around $50-60.
You're going to spend about $15-$30 a pop for a disposable camera, that is only good to about 40 ft. at most. Housings, like the Reefmaster CL that I was talking about, run about $80-$200. An actual underwater camera can run about $200- on up. The strobes alone can cost at least $100 -on up, and you're going to need one to get good pictures past a certain depth (about 60 ft. I think). You have to decide which one will meet your needs best...but if you plan on being able to get good pictures, I'd pick a camera that allows you to add on strobes and close up lenses, etc.
Maybe this will help