I agree with the comments about the off-site shuttles, with the exception of the Downtown Disney hotels (Hilton, Doubletree, Royal Plaza, Best Western, etc.) on Hotel Plaza Blvd. They have regular shuttle service, while off-property shuttles can be erratic, and if you miss your ride back, you've got a problem.
Car rates, especially last minute, seem to be pretty attractive right now, so I would consider looking. However, unless you have an AP, you'd have to pay parking each day.
Also, consider staying on site...maybe at an All-Star. Bus service is regular and you don't have to deal with a car, transportation to/from the airport, etc.