One way to make EZpass work in FL
There is another solution, which is little-known, but works to unite EZPass and SunPass...
I needed a new EZpass transponder 2 years ago (I live in VA, an EZPass state) anyway and had a trip to FL planned so I looked into the options and discovered this solution while being tired of waiting for the full inter-operability.
North Carolina's entry into the toll tag game, "QuickPass" works on both the EZPass network AND Florida's SunPass network (as well as Georgia's "PeachPass" system, although I've not tried that). Thus, virtually any toll system from Maine to Illinois to Florida (even NH now which was one of the last EZPass holdouts...) can be paid. NC doesn't have many toll roads (only one can I think of), so perhaps they have been more aggressive in negotiating agreements with other states.
At the time, it was the only pass offering that did this. To my knowledge, that's still the case.
I can verify it works in the EZPass system (I've used it in VA and all the way up 95 to NY) and in FL (used it in Tampa, Polk County, and Orlando without issue)
I think it's $20 one time for the transponder but no monthly fees. Make sure if you need EZPass you get the regular transponder and not the "sticker".
I am not sure it would be worth getting for someone just to use in FL, but if you live in an EZPass state or travel in EZPass areas it would be a good, flexible option.
Note that it would work in any EZPass toll, it would not allow access to any special local deals (some areas have extra discount plans for certain commute plans and such). For example, it does not take the place of the "switchable" HOV/Toll pass used here in Northern Virginia (you can use the HOV/Toll lane and the toll tag will work, but you cannot "switch it" to ride for free as a legitimate HOV user).