There are many ways to save money on the cruise you plan. The two things that help most are to plan early and to be flexible. Put some research into your planning and compare prices. Select a cruise line that is less expensive than others. Go during the off-season.
Tropical cruises are cheaper in the summer.
Wait until the last moment and bargain with the cruise line. They may be willing to cut the price to avoid vacancies. Deal with an organization that specializes in selling short-notice travel. Decide early so you can get early booking discounts and will have the cheaper accommodations available to you. Some large travel organizations obtain discounted fares because of their huge buying power.