Like airfare and land extensions, another large secondary expense you may incur is excursions during your cruise. Of course, you never have to leave your ship if you simply prefer to stay aboard and enjoy the amenities there, but if you want to explore some of the ports where your ship will call, the odds are good that it is going to cost you extra.
It's hard to generalize about how much each excursion will cost, as they range from less than $50 on some cruise lines to several hundred dollars apiece for higher-end opportunities aboard other cruise lines. Your best bet is to ask your cruise ship staff for literature and pricing on the excursions available during your cruise, or go to your cruise line's Web site for a detailed list based on your sailing dates.
Some cruise lines, such as Swan Hellenic, include a good number of excursions in the price of your vacation, but for the most part you should expect to pay extra to do anything and everything you would like to on land. Even when some excursions are included in your overall rate, others will be offered to you that might be too hard to resist.
The most important thing to remember about shore excursions is that they fill up fast. If your cruise ship lets you book excursions in advance of actually getting aboard, take it—by phone, by Internet, by carrier pigeon if necessary. And if you find yourself squeezed out, get on the waiting list. People do change their minds at the last minute.
Some cruise lines, such as Holland America and Crystal Cruises, will even let you customize your excursions instead of always staying with groups from your ship. Crystal has a Land Programs Department that will do everything from extending the excursions already available (such as adding a private helicopter ride to a group hike) to creating a private excursion just for you (such as a one-on-one, behind-the-scenes tour of the Vatican).