Hi I would suggest you go to the Mousesavers site and in the search area type in car rentals. They have discount codes listed for different companies. Try them out, we found a great discount code to use in late December with "Avis" but there were others as well. Good Luck.
I got a good rate on a car with Alamo using one of the Wal-mart customer corp. id codes (iI think it was rate code BY and ID# 428448 or ID# 430710) at Mousesavers along with a code on the Alamo website for $15 off a weekly rental (Coupon Code: D42C)