If you don't have a transponder, or yours doesn't work at your destination, you can always buy one. In Florida, for example, a SunPass Portable transponder costs $19.99, or you can get by with a SunPass Mini Sticker transponder for just $4.99. You can buy them at Publix, CVS and Walgreens. Both units allow motorists to have tolls electronically deducted from prepaid accounts. SunPass also has a helpful page for car rental customers.