We just booked a 7 day cruise out of Port Canaveral during school vacation week in the Northeast for Feb 2018. 4 years ago we book the pretty much the same cruise in the same room on the fantasy. The price was $4,000 cheaper 4 years ago. Did Disney increase their price 80% in 4 years? It certainly seems so.
Prices have risen sharply over the past 4 years at
DCL, particularly for cruises during school holidays, so if the cruise you're talking about covers President's Day weekend, that will make the price even higher.
If you also go to Walt Disney World, you'll notice a similar level of price increases at the Disney parks and resorts. Like the parks, the
Disney Cruise Line adds special events such as Star Wars at Sea, Halloween at Sea, Marvel at Sea, and Merrytime Cruises to increase bookings & prices during some parts of the year. Also, the Fantasy is much more expensive than the Magic or Wonder. If you want a better deal, sail off-season (when there are no school holidays scheduled for most of the U.S.) on a "classic" ship (Magic or Wonder) that is not hosting a specially-themed sailing.
Mid-to-late January or September (prime hurricane season- watch out) on a ship that is not doing a themed sailing is probably your best bet for lower pricing. Book it on or shortly after opening day, not several months after bookings on it have been open, for the best pricing, or try to nab a GT restricted rate during the last month or two before sailing, if one pops up.