go here:
http://www.desura.com/games/dominion...wakening/forum
for dom 3 at least.
in dom 3 priests need mage levels to get benefits from communions. There is a summonable mound fiend. And the hidden in sand and snow spells also summon priests.
And they are not cheap. The h3/h4 spells are not that great anyways. It is better to spam evocations. Giving the slaves bows is cheaper. anyways.