Peter:
I'd recommend checking out National or Alamo because there are two car rental returns on Disney property that are served by them. And one is very close to the Contemporary.
The Car Care Center is just minutes from your resort. The address is:
National/Alamo at the Car Care Center
1000 Car Care Drive
Lake Buena Vista , FL 32830
Phone: (407) 824-3470
Hours: Monday through Friday: 6 a.m. to 8 p.m. and Saturday/Sunday: 6 a.m. to 6 p.m.
Last year, I returned a car there and found the process very simple. Best of all, it had is own shuttle to any park or resort on property. I always caution folks who visit the panel, that the Car Care Center is a little tricky to find, as you go through the gates to the Magic Kingdom and then have to get over into the far left lane to continue on the parkway to the Car Care Center. My advice: get in the lane that's to the far left before you approach the MK gate.
I also found that www.mousesavers.com has a lot of helpful info on not only discounts for National and Alamo but helpful information on renting cars in general.