[Taqwus]

Are you using drain scale? If so, it'd be hard to compensate unless you push for Construction 4 and go with cheap mages (spectators come to mind, as they can forge their own skull mentors and summon the next spectator as well, and don't cost upkeep or supply) plus skull mentors.
Archbishops are expensive. Unless you're needing vast numbers of longdead horse, you probably could use the research and other summons more.