In game, you are seeing the actual beaker cost. This is calculated from the base cost by multiplying by factors based on map size (1.1 for standard), game speed (1 for standard) and (maximum held) number of cities, and as you say reduced for known civs that have discovered it. The base costs are defined in one of the xml files (can't check just now). You can also see them in the civpedia, although the numbers there have been adjusted for map size already, so in a standard game, the base cost is 10/11 of the number shown. In my games, it's not unusual for the actual cost to be around double the base cost.