Alamo has a desk at the Dolphin, and Budget has a desk at the Doubletree in Downtown Disney. You could rent a car at either of those places and return it either at WDW or the airport. I don't know about Alamo, but Budget has a shuttle - they can pick you up at your hotel and take you to the Doubletree when you need to rent your car.
Try DOLLAR rental at Grosvenor Resort(close to DTD), try online and use Promo code KISSE, if asked for Rate code its KISS. ALso you might want to check out Transportation thread to get discount codes.
We're doing Vero first then BWV . I rented a mini van at the airport from Alamo . I used my BJ's membership and got a discount and I was able to use a BJ's coupon too. I'll drop it off at the Dolphin although I could have chose the car care center too. Then I'll walk back over the bridge. Easy as pie!