Josh,
We stayed in Florence for a few days last year. One day we got a rental car to drive to some of the hilltowns and do the chianti rd - 222.
We ended up getting a rental car at the airport, which was fantastic! (we had taken the train into Florence). There's a bus station right by the train station in Florence. We hopped on the bus to the airport and picked up the rental car there. That put us outside the city limits, so it was not difficult to be on our way! That night we returned the car to the airport (easy to find off the autostrada) and had the option of taking the bus back to Florence or a cab. We opted for a cab only becaus we were starving and paying the extra 30 euro or so was worth it!!