If you're a billionaire who enjoys superluxury cruising, you know Aalsmeer, Netherlands, because it's home to Feadship, a storied yacht builder that's been around for more than 100 years.

Feadship's famous customers include Steve Jobs, Larry Ellison and other billionaires willing to shell out $40 million to $60 million for a yacht.

(Read more: 8 towns where you would never expect to bump into a billionaire)

But that sticker shock is just the beginning. The cost to keep these boats afloat is pretty mega, too, according to some yacht experts and owners.

• Docking fees can run $300 to $400 a day.
• Insurance fees can add up to $1 million a year.
• Food, beverage and flowers can set you back between $1 million and $3 million annually.
• And brace yourself at the fuel pump, as the words "fill'er up" can cost you around $500,000 for a single tank of gas!

Total it and you're just keeping your head above water at about $5 million a year.

Throw in some unscheduled maintenance and fit-for-a-billionaire security and you're adding millions more. That may explain the old adage, "The best two days of a boat owner's life are the day you buy a boat and the day you sell it."

—By Ray Parisi, CNBC Director of Specials

For VIP access to Amsterdam's secret world of megayachts, get on board with "Secret Lives of the Super Rich," airing Wed. at 9:00 p.m. EST/PST only on CNBC. You can't afford to miss it! Follow @CNBCSuperRich on Twitter.