try to plan your trip to get the cities out of the way before picking up the car. florence charges by the milometer for car parking in the city. you could get to venice, go to florence and rome by train, pick up the car at rome train station, and drive through tuscany. then dump the car at flr and fly home. my experience with open jaw tickets has been quite favorable. i have open jawed nce, par, vce, flr, fco, mil, blq from iad, and never paid a large premium. even par-fco was the same price as both cdg and fco rt. you cannot afford to park in some of those places, but car dropoff is not a problem. e.g. most of the florence drop off places are just around the corner from the two starwoods. no premium to drop off there.

in fact, there was a 10% tax for all cars picked up at airports in italy. have not driven in italy in years. my wife took the keys away when she got someone to convert 240 kps to mph.