The richest of rich people water toys, the Migaloo M5:
165m, 10k ton, personal luxury sumbmarine with air-independent propulsion and a full month submerged endurance with seventy people on board. Also has two surface tenders, four smaller subs, and helicopter.
They want something like 2.3 billion dollars for it.
Edit: I believe the 2.3 billion figure is for the even larger M7. I'm not quite sure what the projected cost of the M5 is.