It depends: what time of year will you go, what do you want to do, will you be staying in a hotel, etc.
We went nearly 2 weeks ago, just my son and I. It was kind of a sudden thing (1 week notice?) because I'd promised the boys we'd go this year, and then my husband's back was hurting, and he couldn't ride in the car 5 hours or walk around the park, we were planning his surgery, we decided to wait until he recovered from that....but then we got the news that they were going to do an additional procedure and it would take until end of August to recover (his surgery is tomorrow). I was like "WHAT?" I don't like heat and humidity. I don't like big crowds. I didn't want to take my children on their first trip to Disney and spend most of the time in lines. I just didn't want that for their first experience (that's not "magical" to me, LOL). He starts school end of August, so we decided suddenly to go a week before we did, so we could hurry up and go before school let out (the crowds surge into Disney on school breaks), or before it got too hot. It was just me and my son. I got on orlandovacations.com (I think that was it) and found a great deal (still off season) on a hotel very close for 3 nights. We bought tickets at a discounted price (not the park hoppers---I figured our first time, and my 5 year old son's age, meant we could just take our time and just do one park a day, starting with Magic Kingdom), for 3 days. Instead of a character breakfast we did the Pirates & Pals excursion (a pirates party with treats, cake, all kinds of snacks and drinks, hosted by Captain Hook and Mr Smee, some games, then a ride on a little boat to see an electric light show and then a great view of the castle and watching the fireworks from the water, playing games and singing songs on the boat, and then Peter Pan surprised us when we returned to the dock). All of that combined, about $700. We brought in frozen waters and a frozen gatorade to share, and some fruit (in my backpack). We'd go back to the hotel in the heat of the day and eat sandwiches, celery sticks and hummus, drink lemonade, and have a nap before getting back out there and tackling the park some more, so we didn't pay for anything special except going out to eat in the evenings (I guess add $50 or 60 for 3 evenings of eating out). We didn't do without, we were perfectly fine and happy. It's not "cheap" but we had an excellent time with a week's notice and $760. The key for us was to be prepared, and go off season. I'll take my other son (he's little) in late October or early November for his 3rd birthday, while my older son is in school. The older son is cool with that, understanding that my little guy didn't get to go with us because Daddy wasn't able to come and help....and we had a great time just the 2 of us, and it'll be my little guy's "turn" come fall. He's too little to stay up happily for a Pirates & Pals thing, but we'll do breakfast with Mickey or whatever for him. Just in case, I'll reserve it a month out, for 2 days (not sure about when schools around the country let out for fall break).