Oh, another thing I also mentioned in another thread but I'll repeat for the benefit of anybody reading this one. There are several blood magic sites which give you a significant (40-60%) reduction in cost to rituals. I think a lot of people neglect searching for blood sites because they are a lot less common but just think about the impact of having a 60% discount while pulling in 100+ blood slaves per turn. It's worth some effort to look for.
