Our cheapest trip was last July 2013. I was starting Nursing School in August and we wanted a vacation because we knew we wouldn't be able to manage one during the next two years. We also wanted to make it a budget vacation since I was changing my job, cutting my hours and my pay, and investing in my education.
I used Disney rewards we had accrued over two years.
It was enough to pay for 5 nights at Ft. Wilderness .We tent camp so we were in the cheapest sites they have. (Before you panic, yes, we brought a window A/C unit to cool the tent. But, we ended up not even using it, the nights were perfect, lol).
The rewards also covered 2-day tickets with water parks and more (so four park days), and $160 left over for spending cash (which we used to snack around World Showcase in Epcot and for some lunches at the water parks, if memory serves).
We bought groceries at
Walmart on arrival in Orlando which ran about $160.
Plus gas for the drive from Indiana to Orlando and back. I honestly can't remember how much that was, but we drove an Impala so our mileage was decent. We also boated at Ft. Wilderness which was maybe $40??
So, around $400 for a family of four (including two teens).

The kids did bring spending money of their own to pay for some souvenirs.
I know this isn't some people's idea of a fun way to vacation, but we LOVED it. The Ft. was awesome and the trip was so relaxing. A much different feel than our two prior trips to the world (10 days in 2005 and 14 days in 2010).
Technically, we did have three more days at Universal staying at the Royal Pacific during that trip. This added quite a bit more to the total cost, but I wanted to break the Disney portion down since that was what the OP wanted to know.
We paid $600 for 3-day park-to-park tickets at Universal.
The two nights at the Royal Pacific was covered by Blue Sky rewards.
We finished off our groceries there, but still bought a couple snacks and meals inside the parks and city walk. Some of that was also covered by rewards card/gift cards we had received before the trip (I had been saving them for a while).
That part of the trip probably added $800 to the total trip price.
So, around $1,200. Family of Four. 7 park days. 5 nights camping and 2 nights at a luxury resort. Gas. Meals. Entertainment. Not to shabby!
Just wanted to provide "full disclosure." lol.