Jim&Martha

Please see this thread in the AVIS forum.

http://www.flyertalk.com/forum/Forum77/HTML/000061.html

FWIW,
Costco discount code on AVIS is A108325 or A108300. On Hertz is is CDP# 336436. I don't know about Budget because I have never rented from them. Sorry.
I recommend looking at all the car rental forums on this board(who you would consider renting from)and see what discount codes are listed and making a list for your personal use. I have saved a lot of money this way. Also be on the lookout for links to $ off coupons that can be printed out. They have been posted on both the Hertz and AVIS forums.