Just about every major rental agency has an office somewhere on Disney property. Most are at the hotels in Downtown Disney, Alamo/National are at the Dolphin and the Car Care Center, and Hertz is at Shades of Green. Although there is no rental office at the Floridian, all of the on-site rental agencies have airport-type shuttle vans that will pick you up at your hotel (or a park) and take you to their office. After the rental, they will take you back anywhere on property.