When I drive, I always park in the Economy Lot at the airport - $8.00 a day. Never had any problems. The busses were quick - However, the last time to Disney (10 day trip), we used a car service - worth the extra $ since we had to be at the aiport at 5am and did not get home until 11 pm.
If you used a TA, sometimes they will have coupons for one of the locations in Essington, etc.