Sao Paolo is not actually a cruise port, but is served by the port of Santos. Combined, Santos serves as the port of embarkation for approximately seventy cruises every year from both Costa and MSC to South America, along with other places.
Overall Sao Paolo is extremely affordable compared to other ports. Check out the illustration below for the average cost per day by month (Cruises only depart from Sao Paolo between March and April). Prices are around the same throughout the year.