Pricing "Costs ER, Fatigue or HP"

[nerdvana]

While I am going to be using RPM for learned magic (Wizard equivalent) I'm also looking to have Magic as Powers for inborn magic (Sorcerer equivalent). I want sorcerers to have to charge their powers internally but not limit them to one source...

The way I see it each magic effect would have an energy cost which can be met at a 1:1 ratio by spending ER, a 2:1 ratio with FP and a 3:1 or 4:1 ratio with HP - they can even mix the sources. Lets say they have an effect which costs 12 energy - they could spend 12 ER... or they could spend 1 HP (using 4:1 for this example), 2 FP and 4 ER if they wanted.

I'm thinking this would be a composite limitation but I'm not sure how to build it.

[nerdvana]

After posting the above I found an answer for myself. PK's article "The Power of Sorcery" addresses my question with a little adaptation.

[Jerander]

Originally Posted by nerdvana

After posting the above I found an answer for myself. PK's article "The Power of Sorcery" addresses my question with a little adaptation.

I'll throw out an answer anyway, just for fun.

Costs FP assumes ER as an additional source of power. Use an Either/or Limitation combining Costs FP with Costs HP, then you have access to all three (FP, ER, HP).

[PK]

I actually wouldn't use either/or rules here, because really this is all just a weird amalgam of one limitation. Costs ER and Costs HP are just variants of Costs Fatigue, after all.

The idea behind an ER (power source) is that you can pay fatigue costs for powers based on that power source out of your FP or your ER. So that's actually the baseline assumption. ("Must use ER, never FP" is worth an extra -5%.)

So what you're doing here is starting with Costs ER, but modifying it so:

Downside: If you want to use FP, you do so at a 1:2 loss.
Upside: You can use HP, though at an even worse loss.

In my mind, as long as the HP loss is as bad as you suggest (1:3 or worse), I think those count as a special effect and cancel each other out.