Found out why. Seems there is a multiplier based on leadership etc, so because your leadeship increases the price goes down.
Won't be able to post an update today for this but my idea is to add the price increase back for the levelling. But have it increase a bit less the for "setup" if @Pieter Boelen wants to make it be my guest. For balance I think you should increase the absolute value in create officer. Then you can reduce the price per level a bit in finish init in leveling.c. And add the same line in the levelup loop but with a slightly smaller number.