You're right, it doesn't appear to add up with those items factored in. There are other factors to consider though. The onboard revenues from the drinks, the shops, the spa, shore excursions etc, add up very quickly. When you add all of that in, and the fact that most people do pay more than $700 for a 7 day cruise, I would guess the average daily expenditure would be closer to $200 per day per person. And then there's the airfare, and pre and post cruise packages that some people book through the cruise lines that provide additional revenue.
Also, I'm guessing these ships are not 100% financed, and the interest on what is financed can be written off. The older ships in a fleet that are paid off, provide ample cash flow to the company as well.
These are just my thoughts. I am not an accountant either, and can't pretend to know the cruise lines accounting methods.
Here's a link to Carnival's financial statments. Take a look at the income section and you'll see revenues, costs, interest they paid,,, all totalling to a net income of over a billion dollars in 1999.