Meet the Fathom One: a modular underwater drone that lets you explore any body of water without getting wet. This HD water drone has detachable thrusters and can be customized and upgraded. You also get an integrated rail system to attach cameras, lights, and other sensors.
Fathom One has a max speed of 3 knots with a max operating depth of 150 feet. It has built-in 3W LEDs for a clear view at night. Will ship for under $600.