Beijing is served by the port of Tianjin, but is not itself a cruise port. Combined, Tianjin acts as the departure port for just fifteen cruises yearly from Royal Caribbean to Asia.
Cruises departing from Beijing during the the peak season of summer are much more expensive than the the low season of fall. Overall cruises from Beijing are fairly expensive compared to other ports. Check out the graph below for the average cost per day by month (cruises only depart from Beijing between August and October).