Approximately 1993 or so Budget had a promo where if you rented a car 5 (perhaps as many as 6, I can't remember for sure) you received a totally transferable free coach R/T on AA, for most participants the free R/T was good for travel only in the continental US however if you were a Hawaii resident - which I was at the time - it could be used between HI and the mainland. I lived about 3 miles from Honolulu Intl at Hickam AFB, would pop over and rent an econobox for about $25, drive it home and let it sit in the driveway until I returned it the next day.

Maybe not the best promo of all time but still pretty good...