The first trip to WDW is so very exciting! It is overwhelming.
Some ways to conserve on the budget: Bring your own lunch to the parks, or your own snacks, or at least your own water (or bring little packets of flavored drinks to add to the WDW fountain water). Disney will allow you to bring in soft sided coolers. No glass containers or alcohol, but anything else pretty much goes.
Use counter service dining instead of full table service. It will cost less, and you will be able to share many of the selections. Or, you can order a child's meal (if they appeal to you) from counter service. If you want to do a full service table meal, plan on doing it for lunch as many of the restaurants have the same menu for lunch only at a lesser cost.
Drinks at Disney are expensive. From water to beer to wine, to whatever, you are going to be paying MUCH so try to defray that cost whenever possible.
Tickets are tickets. You'll want to make the best choice. If you don't pay for the park hopper feature, then you will do one park per day, and one park only. That works sometimes! I paid for the park hopper feature for a guest, and we ended up never park hopping! If you don't want to pay an extra charge for your ticket never expiring, be certain that you purchase only enough days to use for this trip.
Cirque is wonderful (and expensive). Well worth doing though, so go and enjoy!
Trim your souvenir budget to the bone. You can purchase some very nice things (usually, but not guaranteed) at the Disney outlet store at Premium Outlets (very near DTD).
Will you have your own transport? If not, you'll really want to consider staying onsite. Often, you can get a really decent rate at the value hotels. They are LOADS of fun! They also have food courts (the All Star Resorts have the best, in my opinion) which help tremendously in reducing your food costs.
Disney is a huge place with so very much to do, you will be amazed. Do be certain to get that good guidebook, and know what is available in each park. Have a rough itinerary of what you would like to accomplish in each park, but keep yourselves open for the unexpected and spontaneous events!
The time of year you plan on visiting will have much to do with the way you plan your days.