Florence is served by the ports of Livorno and La Spezia, but isn't actually a cruise port. Added up, Livorno and La Spezia functions as the departure port for twenty cruises every year from both MSC and Costa to the Mediterranean and Europe.
Cruises scheduled from Florence during the the peak season of summer are significantly more expensive than the the low season of fall. On average cruises from Florence are somewhat affordable compared to other ports. See the chart below for the monthly average cost per day (cruises only depart from Florence between July and November).