Here's a seriously cool DIY toy I'm sure someone here may be curious enough to construct.
Monterey Bay Aquarium Research Institute in California undertook a project a few years ago to create a relatively cheap alternative for underwater photographic research. The goal was getting more cameras into more hands. The parameters where an open source designed system for DIY construction utilizing off the shelf consumer products anybody can buy. Cost is down to about $3,000 and the system is currently working as designed in a variety of environments. They are currently working on replacing the controller with something even less sophisticated.
Press release here and link to build page below
New SeeStar camera system allows researchers to monitor the depths without sinking the budget