There are non-super, regular yachts that are actually "affordable" in some parts of the world. A 4-cabin yacht (retail about $3 million) with a captain and a steward/cook will cost something like $20,000 to rent for a week in Croatia so you can cruise the Adriatic and visit places like Dubrovnik and Venice. If you consider splitting the cost amongst 4 couples, $5000 for two is about the price of a very luxurious cruise on a major curise line... and here you basically get your own ship and crew.
Is it mustachian? Probably not. Is it a better experience if you were going to drop $2500 per person on a 1-week cruise anyway? Definitely. I prefer cruising in the $300-600 per person range, but who knows, someday my tastes may change.
And remember the Millionaire's 3-F's rule... If it Floats, Flies, or F***s, it's cheaper to rent.