I'm not sure how much Magic Kingdom costs but when I was planning my dream wedding reception I looked at how much it costs to rent part of Hollywood Studios for the night. We love Hollywood Studios and looked at Pixar Place or Great Movie Ride as an option as the place to have the reception. The price for Pixar Place is 2,000 venue fee with an additional 5,000 food and beverage minimum. That is 7,000 just to have the area for the night and not any rides. Just to have Toy Story Mania open for the even is 8,500 more.
I've heard you can add additional rides to be open for anywhere between 3,000 and 17,000 more dollars per a ride. Also you can throw in a late night parade for over 30,000 and fireworks for over 15,000. I have the brochure still is where I am getting these numbers.
So yes for the right price Disney will rent you anything but it is pretty expensive if you want the whole package. Their venue rates are pretty competitive but throw in a ride and you are going to be shelling out.