Hi! Congratulations on planning your first vacation to Walt Disney World. While you are there, make sure you visit guest relations at one of the theme parks to pick up your 1st Visit button!
I have many suggestions for budget-minded families! Many of them are outlined in this post
HERE.
You didn't mention if you are interested in staying at a Walt Disney World on-site property or an off-site property. Keep in mind that if you stay on-site, you will likely not need a rental car, which can result in some savings. I'd recommend you price out a variety of options and decide what works out the best for your family.
If you do choose to stay on-site, you may want to consider purchasing a Disney Dining Plan. I enjoy having the dining plan because I know in advance what i will spend. Even if you don't have a dining plan, you should set a meal budget and stick with it.
In addition, set a budget for souvenirs. There are so many great Disney souvenirs, so make sure your girls each have a dollar amount they can spend.
Also, in advance of your vacation, pick up a few guidebooks, and decide which attractions are "must-sees" for your family. In my family, the planning is half the fun, and all it costs is the price of the guidebooks!
Have fun!
Have a great vacation!