Originally Posted by
guv1976
"I am trying to avoid ... exorbitant "convenience fees" for the tolls."
Have you considered purchasing your own personal SunPass to use in your rental car? If you can find a reasonably-priced one-way rental from MIA to FLL/PBI, that's probably what I would do -- especially if I had the amount of luggage that you will have.
Link to SunPass retailers:
https://www.sunpass.com/sunPassRetailers
(Of course, if you rarely drive in Florida, the initial $19.99 cost of a SunPass transponder might make this an unworkable solution for you.)
There is also the $5 tag that sticks to the window that could be a one time use thing.