Bangkok is not a cruise port, but is served by the port of Laem Chabang. Added up, the cruise port of Laem Chabang is the port of departure for only one sailings annually from Norwegian to Asia.
On average sailings from Bangkok are somewhat expensive compared to other ports. Prices are around steady throughout the year. Look at the chart below for the average cost per day by month (Cruises only depart from Bangkok between February and February).