That is cool!
From there website:
"Price for a custom built Seabreacher is dependent on the number of options that a customer chooses, but price tends to range from US$ 65,000 for a standard model to upwards of US$ 85,000 for a high-performance, heavily customized version. We have an extensive list of available options, but any specially requested options can also be considered."
It works like a regular submarine- you use the bow planes to force the nose down. Only difference is this is much more bouyant so it pops back up again. This is pretty old though, posted back in April..
How did they get it to submerge and keep the engine running???
Same way you can submerge any other PWC, its just some kind of baffle i think. The engine doesnt breathe air from outside the craft, it breathes it from the inside.