I just went to the wdwinfo.com transportation page, clicked on Rental cars then on the ad marked
Budget DIScount; put in your dates but put the pickup time as being the day after arrival, at 9am, then returning it the night before your depature at 6pm, to the DoubleTree near Downtown Disney (8 minute walk) and it dropped a full size (2/4 door) to $190.
This is assuming you don't mind walking the few minutes over to the Doubletree from Downtown Disney and that you're willing to let Disney's Magical Express drive you from and to the airport. Of course that's also assuming you're staying on site...
Regardless....play around with that DIScount....we just did it two weeks ago and I was very pleased with it.