Beijing is served by the port of Tianjin, but is not actually a cruise port. Combined, the cruise port of Tianjin acts as the port of embarkation for only ten sailings every year from Royal Caribbean to Japan.
Prices are around the same throughout the year. Overall Beijing is rather expensive compared to other ports. The illustration below shows the monthly average cost per day for cruises from Beijing (Cruises only depart from Beijing between April and June).