[Digress]

I didn't want to give the impression that I think the slayers are a huge issue - I just think for "flavours" sake they could be summons (with high upkeep - think of all the beer they drink and associated damage these dudes do to the environment/taverns).

Small gem cost + small research cost + mage time = Slayers + upkeep

I think the way Sombre made the upkeep for the Skaven Globadiers/Warplightning Crews etc. high works pretty well.

I do think the Runeguards could be given some cold resistance - these guys are staunch.