Here is the information on the car rental toll programs. Looks like with
Alamo you are charged $3.95 per day that it is used plus the tolls.
https://www.sunpass.com/en/tolls/rentalVehicles.shtml
You may want to look into this. It's new and it is free to use - you just have to pay for the tolls. I have not used it myself yet, but after seeing a couple posts about it on here am going to try it out for our upcoming trip this month. This is only applicable if you are renting from and returning the car to MCO.
https://www.visitortollpass.com/
If you are only in the Orlando area, it looks like there is only one toll road that is strictly pay by plate. If you are leaving the area and going tom Miami/Fort Lauderdale area you will definitely encounter this. But everything else in Orlando area (at least according to the Sunpass website) has cash lanes too.