On package vacations, single travelers are often hit with a "single supplement" to the base price. To avoid it, you can agree to room with other single travelers or find a compatible roommate before you go, from one of the many roommate-locator agencies. This is also a good way to avoid the relatively high cost of a double room-single use, as opposed to splitting a double.
Note: This information was accurate when it was published, but can change without notice. Please be sure to confirm all rates and details directly with the companies in question before planning your trip.