do you rent the car at one of the resorts?
A one-day car rental might cost a little more than a round-trip taxi ride, but it's a much more flexible option. It will allow you to go to more than one place for shopping, dining, and grocery stops.
There are two places on Walt Disney World (WDW) property to rent a car: the Disney Car Car Center, which is a stand-alone facility near the Magic Kingdom park (MK), and the Dolphin Hotel, which is a non-Disney hotel in the Epcot resorts area. Both can be reached from All-Star Movies (ASMO) via the WDW transportation system (buses, boats, and monorails). Both are rental locations for National and
Alamo (which are both owned by the same parent corporation and are the official rental cars of WDW).
There are also rental counters for several other agencies in the hotels on Hotel Plaza Blvd, which in in the Downtown Disney area. These hotels are not on the WDW transportation system, but are reachable by taking a bus to Downtown Disney and walking a short distance.
For my money, the convenience of renting at one of the on-site Alamo/National locations is worth a few extra bucks.