Avis $2.95 fee per rental day plus tolls (at posted cash/TOLL-BY-PLATE rates)
$14.75 maximum fee per rental month (30 days) plus tolls (at posted cash/TOLL-BY-PLATE rates)

https://www.sunpass.com/rentalcar

now you could use the cash lane - however some have had problems where they paid the toll by cash and were still charged the toll fee by the car company because it was a sunpass lane as well (the transponder was not turned off) - also some areas of Florida do not have cash lanes any more.

At Avis - if you use the toll roads early in your trip and not at all for the rest of it - you are still charged 2.95 a day even if you don't use toll roads on those days. http://www.avis.com/car-rental/conte...001366#Florida

These fees and toll discounts may be insignificant to some, but for us that was 2 beers at Epcot World Showcase!