I've never cruised before so I got the Carnival brochure but they did not list the single supplement price. Is it 150% ?? and I heard you can purchase a fountain card good for unlimited soda YUM YUM. How much does the card cost??
First off, don't read the brochure's prices and think that is what it will cost you to cruise. They are WAY overstated. Brochure price for my upcoming cruise was $799 but I paid $291 through a TA. I don't think anybody actually pays brochure rates.
Second, the single supplement changes along with the cabin price. You have to keep on top of this and check back often to get the best deal.
I would recommend two things. Post your desired cruise in the bargain finders feature of this website. TA's from around the country will contact you by email with their offerings. The other thing would be to post in the Single's forum or Seeking Cruise Companion forum. You might find somebody who wants to share a cabin or learn of a special sale going on for singles.