If you think that landscape or portrait photography is expensive, just wait till you investigate underwater photography. Depending on your camera, you may spend upwards of 5-6 times the cost of your camera to house it and equip yourself with strobes. Ouch!!! The first element in deciding about whether to enter this field is financial. Do you really want to spend the money?
Going through all this, I settled on a mid-level system that doesn't have the best camera or all the features, but cost me far less than the BMW of the class. You can easily spend $20,000 on an underwater system. I chose to spend about $2,000. That is for a nice point and shoot (with all its inherent problems) and an inexpensive housing.
Canon G9 System