Dollar is located at the Wyndham across the street from DTD. And
Avis is located at the Hilton that is a 5 minute walk to DTD. We have rented from both companies and we just take the DTD bus back to the resort when we are done with the rental car.
here is the link to the "sticky" with all the info about rental company at or near WDW.
http://disboards.com/showthread.php?t=2927109
We had a friend going from CLE to Denver on Frontier who got stranded at the airport for a day and a half a few months ago because his Frontier plane had a mechanical problem. Frontier has such a small fleet of planes they did not spare plane to take the place of the broken one so they were stuck waiting for the next time Frontier was scheduled to fly into Cleveland. Lucky for them there was room on the next flight for them. Did I mention they waited a day and a 1/2 for that flight to arrive! And that is the reason we won't fly on airlines with a small fleet of planes. All is takes is on hiccup in the system to throw off your travel plans.