Beijing isn't a cruise port, but is served by the port of Tianjin. In total, the port of Tianjin functions as the embarkation for thirty cruises yearly from Royal Caribbean to Asia.
Overall cruises from Beijing are fairly expensive compared to other ports. Sailings leaving from Beijing during the the peak season of summer are a bit more expensive than the the low season of fall. Check out the illustration below for the average cost per day by month (Cruises only depart from Beijing between June and October).