I actually contacted Disney Catering and Conventions first, and them they put me in touch with an Event Planner at the Grand Floridian.
I do know that for small groups, they can arrange things in different locations through Private Dining. That just wasn't an option for us because our group is so large.
My EP told me that they have done things from $250.00 all the way up to WAY WAY more!!
She even told us all about one party they did last year that a guy had for his sister's birthday. It was a Haunted Mansion theme, and the price tag was somewhere in the neighborhood of $60,000!!
Don't give up! No matter what the budget you're working with, I'm sure they could come up with something to fit your needs!
If you have a particular resort in mind, I would call and ask to speak to someone in the Catering and Conventions department.
Oh..and do it SOON! It has taken me MONTHS to get through the whole planning process.