Depending on the time of year you decide to go, you can save a lot of money. For instance, avoid peak seasons such as summer and holidays. Instead, go during the "off-season" such as September through November or January though March, excluding spring break. These times are considered the lower seasons at Walt Disney World and can allow you to afford to stay longer, at a better hotel or other options.
Check out the tickets and options you want as part of your package. Disney's ticketing package is called, "Magic Your Way." You basically can choose what you want or what you don't want on your package. You can opt for just the base tickets which allow you to get into one park a day or add on park hoppers which allow you access to more than one park a day. You can also add on the dining plan which comes in a variety of options from the quick service plan that covers just counter service or fast food options to the deluxe plan which covers a variety of options.
Check out the Disney Dining Plan. This is a great way to stay in budget. The Disney Dining plan is a pre-paid option which offers a variety of places for you to dine in the resort without breaking the bank. There is the Quick Service Plan which covers counter service or fast food eateries all over the parks and resorts. There is also the Basic dining plan which allows both counter service meals and table service or sit-down meals.
Another great way to watch your budget is to put money on a Disney gift card. You can put anywhere from five dollars to $1,000 on a card. The Disney gift card can be used for dining, shopping and can also be used at Disneyland, Disney Cruise Line and any other Disney-related shops and attractions.
Keep your eyes open for discounts. Periodically, you will find discounts offered on the Walt Disney World site. Also, check into such sites as disboards and intercot which can be a wealth of information.
Consulting a travel agent can help you as well. Some travel Agents can help you find discounts and apply them to your reservation after you have booked. Some of the most reputable Disney travel agencies are Magical Journeys and Dreams Unlimited.
If you have AAA, you may be able to find some great discounts with them as well.
