Billionaire adventurer Richard Branson's name has already been mentioned on our list, because it's his 'Virgin' company which is selling tickets to outer space to people like Katy Perry and Ashton Kutcher. Branson is something of an eccentric, who owns planes and trains in the United Kingdom, as well as a cable TV company. He once tried to become the first man to float around the world solo in a hot air balloon, but when that didn't work out, he turned his hand to exploring below the seas instead.
Branson bought the Necker Islands group in the British Virgin Islands, and then purchased a submarine called the 'Necker Nymph' to explore what lies beneath them. Nobody knows for sure how much Branson paid for his vessel, but if you want to see it for yourself, you can rent it from him and take your own tour of his islands. All you need to do is contact him to make a booking, and come up with the $25,000 per week hire cost.