The Caribbean's tired, and the Bahamas have been done. Cruisers willing to fork over the big bucks tend to head to more exotic waters aboard small ships that offer either over-the-top luxury or expedition-style learning.

An ultra-expensive itinerary is often only available a few times a year, maybe even just once.

“From a passenger perspective, our most expensive voyages tend to be in the Baltic,” says David Morris, Executive V.P. of Worldwide Sales and Marketing at Silversea Cruises  ”Many guests want to visit the Baltic, but the region has a relatively short cruising season. As a result, not much discounting is needed to fill the ships.”

True enough. The seven-night August 11 sailing aboard the 382-passenger Silver Shadow out of Copenhagen is going for $890 per person a day, and that’s for the lowest category suite—a ritzy 287-square-foot abode with a marble bathroom, walk-in closet and private veranda.

Mary Jean Tully, Chairman and CEO of Ontario-based Cruise Professionals, concurs with Morris. For her business, Baltic and Alaska cruises tend to be expensive. Cruises including Dubai are also going for top dollar. Antarctica sailings, generally offered between only December and February, typically trade at high per diems as well.

Just look at Lindblad Expedition’s 23-night Antarctica cruise next February. Starting rates come in at just over $650 per person a day—and for good reason.

“Ultimately, it’s the quality of research personnel and equipment that makes the difference,” says Sven Lindblad, president and CEO of Lindblad Expeditions. The company spent two years researching how to safely allow passengers to kayak in Antarctica. Aboard the National Geographic Endeavour, they use a super sophisticated ROC (remote operated vehicle) for deep-water exploration and filming.

In justifying the hefty price tag for the Silver Shadow’s Baltic sailing, Silversea spokesman Brad Ball points to three factors: the season (August practically guarantees great weather and calm seas), the ports (three full days in St. Petersburg), and the cruise length. A one-week sail from Saturday to Saturday is very appealing to busy executives with limited vacation time.

Mark Conroy, President of Regent Seven Seas Cruises, says expenses also play a part in setting cruise fares. Tahiti and Antarctica are pricey because everything has to be imported, particularly fuel. Alaska cruise expenses are steep due to high port, pilot and government charges. Transits of the Suez and Panama Canal also come with substantial fees.

“To give you an example, our 50,000-ton Mariner with 690 guests pays $150,000 to transit the Panama Canal, which comes to almost $220 per guest,” says Conroy.

Itineraries that cost big bucks are often packaged with correspondingly expensive shore excursions. During the Wind Surf’s pricey May 20 cruise along the French Riviera, the ship was anchored off the shore of Monaco for three days during the Grand Prix. For $1,900 per person, guests were able to have reserved trackside seating for the time trials and the final race, plus private receptions and commemorative souvenirs.

Of course, there’s also the one-upmanship factor that motivates people to choose their cruises. Like handbags, cell phones and sports cars, cruise itineraries go in and out of fashion for all kinds of reasons. The pace of booking tends to reflect what is hot at the moment, Conroy says.

For some, what’s hot is drinking champagne and doing the New Year's countdown while sailing among the well-trodden, not-so-exotic haunts of the Caribbean. Seabourn’s two week-long cruises over New Year’s Eve aboard the small and stylish Seabourn Pride and Seabourn Legend are going for no less than $699 to $2,078 per person per day.

To identify the most expensive cruise itineraries, we calculated per diem rates, based on double occupancy, for each cruise so that length of cruise wasn’t the deciding factor. We based the comparison on each ship’s lowest-category cabins and we only considered vessels that had the capacity to carry 30 or more passengers.