You won't have to max out your credit card. Most cruise lines, including Carnival Cruise Line, Norwegian Cruise Line, and Royal Caribbean International, require only a deposit when you book, and the amount varies depending on the length of your cruise. For example, on Norwegian, a deposit for a two- to six-night cruise in a standard cabin is $100 per person. On Carnival, the required deposit is $100 per person for a three-night cruise, with the amount increasing for longer cruises. The deposit amount can vary according to the itinerary as well. Deposits for Alaska cruises on Carnival, for example, are $400 per person.