I think you should have a free rental coming as well as an apology from Avis. Actually, you should have a free car, a nice one, delivered to your house. And the employee who took your reservation should be fired. No, beheaded. And Avis should mail his or her head to your house as proof. And the dead employee's house should be sold at auction, and you should get the proceeds.
Be reasonable, for goodness' sake. Someone made a mistake. The difference between getting peeved and going berserk ought to be demonstrable negligence. There isn't any here -- just honest human error.
The more reasonable you are, the more you'll get from Avis. I dropped a polite note this summer after finding the Preferred booth at MHT closed on a Saturday night when it should've been open, and they sent me a bunch of discount coupons. Your insistence on a firing over a no doubt innocent mistake puts you in a very special category... the pass-this-letter-around-the-office, wow-can-you-believe-this-guy category.
Enjoy Hertz.