When you rent a car in Florida, there is a transponder on the windshield called SunPass so you have the 'convenience' of a pre-paid toll when going through the a toll plaza. When you get to a place like Miami, you have the interstates and the Florida turnpike crisscrossing up and down the whole coast as you approach the major cities and many of those ramps charge you a toll but there is no toll booth. It is a camera recording either your plate # or deducting from your SunPass transponder automatically. You might not even know you went through a toll area!
Well, it is not free to use the rental car transponder. It is $15 to use it for EVERY toll. The toll fee might only be $1.25, but Budget will charge you $15 well after you've turned your car back in-- you just see that charge on your credit card statement a month later. If you turn off their transponder and sail through the tolls without paying, you will get billed by Budget $3.95 per day plus the toll fee-- that toll booth could cost you $100.
The problem is that many of the tolls are automated so there is no place to pay cash if you wanted to just do that. I would suggest if you are going to be renting a car in Florida, especially the Miami area that you buy your own SunPass and affix it to the windshield and turn off the rental car transponder. You can buy a SunPass sticker at many outlets like Publix supermarket. It is $4.99 for the sticker but then you have to go to the website and register the sticker and load some money on to it ($10 minimum when you activate the SunPass). You can choose the option to have the SunPass automatically charge you another $10 when you are running low on your SunPass. You might end up leaving a few bucks on your SunPass if you are just a tourist, but that is way better than getting a huge nasty surprise from the rental car company down the road. They all seem to be looking for ways to maximize their revenue, and this toll situation is a cash cow for the rental car companies. Costs them $1.50, costs you $15...