Use Costco to rent your cars. I had a sold out situation like that - in fact, there were 13 people ahead of me at Budget who had also been left high and dry. I called Enterprise, rented a car for slightly more, and when I got back I sent a note to Costco about it. They not only got Budget to refund me the difference, they sent me a Costco gift card as well. I do all my rentals through them now.