SunPass transponders are already installed in many rental cars. You will be charged on daily basis by the rental companies for these devices and this charge may or may not include unlimited tolls. You can opt-out of renting this device if you wish, but please note that in many cases this transponder is fixed to the windshield of the car and can not be turned off. Therefore, if you pass through any toll booths, even if paying in cash, you will be charged for the toll in addition to a hefty penalty by the rental company.