Hammacher Schlemmer offers a cool Five-Person Exploration Submarine.
The sub is on a dual-pontoon structure and housed inside a 3 1/4 inch thick acrylic pressure sphere and can descend down to 656 feet.
Inside, you can keep track of depth, internal pressure, temperature, battery status, thrusters, trim tank status, etc.
2 horizontal thrusters propel the sub at a speed of 2.5 knots.
The battery life lasts for 8 hours and you better know damn well how to use a VHF radio.
Purchase includes training.
Five-Person Exploration Sub ($2.7 million dollars)