When I've done it, it has not been a hassle. Actually pretty easy. Collect your luggage, up an escalator to the people mover train, 2nd(?) stop is the car rental. Counters are right there if you need them, or follow the signs to the garage (just look at the signs so you get on the correct escalator), then get your car and go out.
They even have a pull off before you get on the road to set up your GPS (if so needed).
Big bonus (at least for Delta)... they have a luggage check in location AT the car rental center. So after returning your car, you can check your luggage right there before getting back on the train to the main terminal.
As far as "fees", this is why it's important to factor everything in. If you weren't going to rent a car in Orlando, renting in Tampa cuts into any airline savings. If you were going to rent in Orlando, then price out the difference.