This, all day long, I always stay just north of Tampa, in Hillsborough, Pasco, or Hernando counties, and the tolls on the Sunshine Parkway are worth it, alternatives are US 19 or 41.
I’ve not used it, but I think the Interstate from Tampa to Orlando is I-4, and I’ve been told, but I don’t know if it’s true, that it’s toll free, but that you may encounter tolls when leaving the Interstate at the Orlando end.
You can spend more on gas by taking back roads to avoid tolls, plus constantly stopping at red lights.