I was thinking like an old baja sidewinder, with a big outboad on it, like a yamaha 175 or something....
http://memimage.cardomain.com/ride_images/3/2093/2121/30231060001_large.jpg
pretty inexpensive and fast as fawk. yet you wont flip and die like the one you posted, and a LOT more easy to control.
that being said, jetboats can be fun too, we had one (glastron). (a lot bigger than that piston death trap you posted, lol) use to make it rooster tail and screw with people when tubing/skiing, etc...