A while back someone posted regarding differentiating Summoning- the fact that devils, angels, and faeries would operate differently (I looked for the post but couldn’t find it). Also, the poster was dissatisfied with identical prices (e.g. soul) for the different orders. Anyway, I found this website yesterday that covers this very subject: http://www.mythopoeticgames.com/games.htm
If you download Danse Macabre Core Rules plus the supplements on Angels and Faeries, you’re all set! And they’re FREE.
Covers different entities from the three realms that can be summoned (Heaven, Hell, and Faerie) as well as prices that can be used with each realm. I’m not suggesting tweaking the BW RAW (always a mistake IMHO), just some added flavor for Summoning enthusiasts.