If you're flying to Orlando, you might want to look into Disney's Magical Express. It will pick you up at the airport and transport you to your hotel and all over Walt Disney World, saving the cost of renting a car. You must stay at a Disney resort to use this free service. Staying off-property can save you money, especially if you're traveling off-season. There are plenty of budget hotels to choose from, many of which offer transportation to the theme parks. Keep an eye open for hidden fees and ask about them when making your reservation. Also ask for the lowest price possible. Often there are deals to be had just for asking.
Consider bringing your own food, or buying from a grocery store once you arrive. Many hotels have small refrigerators in their rooms, but if not, use a cooler. Eat a good breakfast, then return to your hotel mid-afternoon for another meal. Walt Disney World also allows guest to bring their own snacks. Granola bars, raisins and crackers are small and easy to carry.
One of the biggest expenses at Walt Disney World is the tickets to the parks. Weigh your options carefully before buying them. Many people swear by the Park Hopper option (which allows you to visit more than one park during a single day), but if you plan to spend an entire day in one park, you may not need it. If you do not want to visit the water parks, don't add that choice to your ticket. Putting more days on your ticket results in a lower cost per day, so if you're planning on immersing yourself in all things Disney, buy your ticket accordingly. When you arrive in Florida, there will be many signs claiming to offer free or discounted Disney tickets. Many of these offers are for high-pressure timeshare pitches, which can save you money if you have the extra time and the resolve to say no.
Items in the theme parks are expensive, and kids seem to want everything. Give them a budget. If they only have a limited amount to spend each day, they'll make their choices more wisely. There are plenty of souvenir shops outside Walt Disney World that are less expensive. Belz Factory Outlet World, 12 miles from Walt Disney World, has two outlet stores with Disney merchandise. Another Disney outlet location is Orlando Premium Outlets, which is near Downtown Disney.
