I've just checked before answering, but saw nothing. Marc answer is what I found. I can understand Jeff's answer, or at least the rationale behind, but it is not in the rules.
Apart to that, I think the rules as written are right: the spell is not provided by the cult, but by the god in exchange of your POW. In the case of a spirit magic spell, the cult is doing the teaching, and it is right to request something in exchange, be it silver or cows, but in the case of rune magic, the god is providing the spell, not the cult.