The unit cost reduction from the Templar Apparent Prestige is not applied to Karax’s Carriers and Colossus, which are still at their default costs of 455/325 and 390/260, respectively.
this is similar to the bug back when karax’s level 1 was reworked where carriers, colossi, etc would not gain 50% increased HP until the upgrade that transformed them into their specialized variants was unlocked