Summoning costs

[chaindog]

I'm using the Game Master's Handbook for sorcerery summoning in a homebrew campaign. For elementals, there seems to be logic in how many MPs it takes to summon one... 1MP per cubic meter which then dictates the elemental's chracteristics. However, looking at the GM Handbook's example demons and summoning costs, there does not appear to be an obvious relationship between summoning cost and demon's power. Am I missing something? In older versions of BRP (such as Chaosium's Elric/Stormbringer), there was a rule that 1 MP per die defining the characteristics and 1 MP per 10% skill was spent in a summoning. Are there any rules like that that apply in MRQ or is a GM is supposed to wing at and guestimate a summoning cost?

 

[Simulacrum]

That's how I read it. So the MP cost to summon a demon is, it seems, an arbitrary call by the creature designer - however it looks like 18 is the top end score for most purposes since this is cited as the highest MP cost to summons a Daemonlord.

Personally I'd like a system to work it out, but there's no real indication in the text why one creature should cost 10, another 12 and another 15.