How much will my cruise be and other cruising questions?

LK asked:

1.Are there any other fees besides the actual cruise rate,government taxes,government fees,and the airport transportation?
2.Oh and is $804 for a four night Caribbean cruise for two on a Carnival cruise a good deal?
3.Any good(active)excursions in Cozumel and Key West.
4.Also how will the food be for me,I don’t expect a very fancy,elegant meal but I don’t want a McDonalds meal either.
5.Any other first time cruising things I should know what I will expect?