Florence is not itself a cruise port, but is served by the ports of Livorno and La Spezia. Added up, Livorno and La Spezia serves as the point of embarkation for just fifteen sailings per year from MSC to the Mediterranean.
On average sailings from Florence are rather affordable compared to other ports. Look at the illustration below for the average cost per day by month (Cruises only depart from Florence between May and November). Sailings departing from Florence during the the peak season of summer are much more expensive than the the low season of fall.