Originally Posted by
RSSrsvp
According to the Hertz site they offer
PlatePass to use on the
FasTrak system for the Greater San Francisco Bay Area Bridges.
You will be charged a $4.95 service fee for each day of the rental
including any days on which PlatePass® is not used, up to a maximum of $24.75 per rental, plus incurred tolls at the Toll Authority's cash toll rate or highest
undiscounted toll rate.
What a ripoff! 
PS, PlatePass is owned by American Traffic Solutions who is responsible for most of the red light and speed cameras in the country.
I travel to the SF area frequently and have one of their FasTrak transponders. I like to register my transponder with my rental vehicle so I don't get a surprise if my transponder does not work. It seems that this is not possible with Hertz in CA as they pre-register every one of their vehicles and this can not be changed. Thankfully, the one time my transponder failed to work I was in a car rented from a different c
mpany.