This is a bit like the length of a piece of string - however, in Florence you should expect things to be somewhat dearer than in most towns in Britain, except perhaps for the diesel. You don't have to use toll roads, especially if you have a short distance to cover into town but for the journey from France it is probably worth taking the toll roads for the convenience and almost certainly shorter journey time. If you are planning to visit the Uffizi then aim to start queueing at the crack of dawn (you can take turns) - arrive in the afternoon and you'll be lucky to get in that day, but it is an absolutely amazing experience if you like classical art collections. Even if you just want to wander around the town, Florence is (in my opinion) a magical place. You would have to be quite unusual not to appreciate and enjoy it.