Just curious....what's the cost of renting a car in Italy? I would think that since you would be walking most of the time when you want to do some sight-seeing, that you would not need the car or it would be a hassle to find a parking space.

Have you looked at the cost of trains between cities and taxis or local transportation costs vs the cost of a rental? Also, if you plan to visit Florence I hear that there are limits to driving within the city.