Lindalee, it depends on your definition of "hidden costs." There are definitely expenses over and above the cruise fare, port charges & taxes you have probably already paid in full. If you have not also booked your transportation from the airport to the pier and back, there will be a cost there, plus gratuities for the baggage handlers. On board, beverages that are included are coffee, tea, milk and juice at meals, and often the same throughout the day in the buffet area (open 24 hours). If you want soft drinks or alcoholic beverages, these cost extra (depends on the cruise line whether the former are an extra charge with a meal), and are comparable to what you might pay in a decent bar or restaurant stateside. The soft drink cards tend to save you money if you drink a fair amount. Other expenses will be gratuities onboard (added to the bar bills, but usually paid in cash at the end of the cruise - the crew members make very small salaries and depend on those tips for their living, so don't stiff them unless they give extremely poor service!), gambling (casino & bingo), purchases in the gift shop, etc.
If you have a Carnival brochure, check the pages of fine print toward the back, as they will outline all kinds of things you need to know before you go - such as what is and is not included in your cruise price.
If you booked your cruise through a travel agent, they should be able to help you with answers to these and other questions you may have. Otherwise, a brochure listing the excursions and their costs should be included in your cruise documents when you receive them, which is usually a couple weeks before departure sometimes earlier if you're lucky. There are advantages and disadvantages to booking your own shore excursions - through the cruise line may cost more (sometimes only a few dollars more) but if your group is late back to the ship they will wait for you (not so if you book one on your own) and if there is a problem with them, you have some recourse through Carnival. Buyer beware can definitely apply. CHeck the ports chat, and those for other cruise lines, on Cruise-chat, and read the reviews, particularly for Spirit, on cruisereviews.com for more info here.
Have a wonderful time! Karen [img]/infopop/emoticons/icon_smile.gif[/img]