Santiago is served by the ports of Valparaiso and Valparaiso, but isn't actually a cruise port. In total, Valparaiso and Valparaiso functions as the port of departure for only one cruises every year from Celebrity to South America and Latin America.
Prices are about steady throughout the year. Overall Santiago is fairly expensive compared to other ports. Take a look at the graph below for the average cost per day by month (Cruises only depart from Santiago between January and December).