Wirelessly posted (BlackBerry: BlackBerry8530/5.0.0.1030 Profile/MIDP-2.1 Configuration/CLDC-1.1 VendorID/417)
"First, and most obviously, joining the Hertz Gold program is 100% free"
Just as obviously, Hertz Gold won't do much for the OP when he tries to rent from
Avis.
There's a recent thread in the FT Car Rental Discussion forum about someone who tried to rent from Budget at the USAA rate and was denied because she could not produce a USAA membership card.