Why?!
We have 2 dogs, 2 hermit crabs, 3 birds and a tank full of fish and we're still going to Disney this Summer.
Our dogs are going to be boarded at the Vet. My dad's secretary is going to be taking care of the birds and hermits and we're putting these feeder things in for the fish.
If you can't afford to take it to a vet or something, then find a neighbor that's willing to dog sit. I'm sure there's someone around that wouldn't mind and you could always bribe them with a Disney T-shirt, pin or something if you really have to.
Or-like the others have said-take it with you and put it in the Disney Kennels. I'm not sure how much more expensive that is...but anything's better than losing a vacation!