Florence is served by the ports of Livorno and La Spezia, but isn't actually a cruise port. Added up, the cruise port of Livorno and La Spezia functions as the departure port for fifteen annual sailings from MSC to the Mediterranean.
Overall Florence is rather affordable compared to other ports. Cruises scheduled from Florence during the the peak season of summer are much more expensive than the low seasons of spring and fall. See the graph below for the average cost per day by month (Cruises only depart from Florence between April and October).