Suggestions for Pricing of Limitations

[Nedorus]

I'm using this post as an inspiration / basis for a summoning ability to mimic that of a well know cyberpunk game (where you shouldn't trust elves or cut deals with dragons).

I'll either use Super-Memorization, Cosmic-Power or the pricing suggested in Powers p. 63 as a basis for pricing. Then adding in:
Limited (Summonable Spirits of your Tradition) -50%
Costs Fatigue 1 -5%
Magical -10%
Requires Attribute Roll (QN), resisted by Will -20%
Maybe some levels of "Reduced Time" depending on the cost basis I decide to use (I want the spirit allies to be reasonably summonable within a single combat)

Now to my question:
I want to factor in two more limitations:
Limited Time: a summoned spirit only sticks around for a limited time; it will return to its home plane when the sun rises or sets
Number of Services: a summoned spirit will return to its home plane when the through with all of the services it owes

These are intended to be "whatever happens first" limits.

The number of services will most likely end up to be the margin of victory (or margin of success) from the actual summoning (Quick Contest of QN and Will)

I'm looking for suggestions on how to price these limitations.

P.S: is there an easy way in the rules to make the FP cost depend on the summoning roll as well? Something like "costs X - Margin of Success"?


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Building the Ability
Here I will update the ability that I'm building for others to reference quickly without reading through the entire thread. I will change but I'll try to always reflect the
latest changes.

Summon Spirit
You summon a spirit of your tradition as a temporary ally. This takes 1.25sec (round up) per 10 CP of the ally summoned. Roll a quick contest of your QN (plus Summoning Talent) vs. the spirits Will. Whether successful or not you loose QP equal to the margin of success of the spirit. The spirit own you a number of services equal to your margin of victory. However the Spirit will only serve you until the next sunset or sunrise and will return to its home plane when all services are used up or the time is up (whichever comes first)

Statistics:
Modular Abilities (Super-Memorization) (Magical -10%; Requires (QN) Roll (resisted by Will) -20%; Social Only +0%; Costs QP (margin based) -15%; Trait-Limited (Summonable Spirits of your Tradition) -50%; Reduces Time 3 +60%)

Cost:
- 23CP for 25%-Starting-Point-Spirit
- 43CP for 50%-Starting-Point-Spirit
- 62CP for 75%-Starting-Point-Spirit
- 101CP for 100%-Starting-Point-Spirit

Interestingly I noticed that the cost doesn't really change much when I change the type of modular ability. +/- 3 points at the low end and +/- 10 at the high end...