The fees of the guided tours are always subordinated to the selected itinerary, to the kind of client (private, school groups, tourist groups from agency) and to the length of the service.
A guided tour of Florence may follow a suggested itinerary, showing the highlights of the city such as: Duomo, Signoria Square, Ponte Vecchio, Church of Santa Croce, Church of Santa Maria Novella, Pitti Palace, etc. Or it may follow a tailor made itinerary off the beaten tracks, discussed together with the client, according to his specific requests.
Besides a guided tour of Florence, including museums (such as The Uffizi Gallery or the Academy Gallery) needs reservations, schedule time to be respected and a better structured development etc. Therefore an approximate price might be misleading and reductive. In any case, as an official tourist guide of Florence I would like understanding exactly the kind of service requested and following the will of my clients, who are always so different, according to their way of visiting the city, the time at their disposal and their interests.