Spells as Advantages similar to D&D's spell-like abilities

[Raekai]

Dilemma. I'm trying to make an Eberron to GURPS conversion and I'm stuck at the dragonmarks. I want to model it closely by doing some kind of spell system which I can't find anything like.

I need a way to price spells in a way that I can make spells only usable once or twice a day. Preferably, I'd like to have them in some kind of advantage form, but not fully fleshed out powers that represents spells. As balanced as that is, it has always seemed too messy to attempt.

Example:
Let's say the Mark of Healing will have Major Healing as one of its abilities. It can only be used twice per day. It also should not require magery. How do I go about pricing this? I was thinking it might have similar rules to that in the Thaumatology: Magical Styles in the way that I might price things by prerequisites or something.

The point is that I'm really bad at balancing things out and I'm afraid to make it over or under-powered.

Thanks!

[Refplace]

For my Powers as magic system I built a core power and each level gave me a Rank. then I built a set of spells that came in at the cost of each rank and bought them as Alternative Abilities.
For the once or twice a day just use that many charges.

[Raekai]

Originally Posted by Refplace

For my Powers as magic system I built a core power and each level gave me a Rank. then I built a set of spells that came in at the cost of each rank and bought them as Alternative Abilities.
For the once or twice a day just use that many charges.

Could you go into further detail? This sounds quite interesting.

[Anaraxes]

Make the spells powered by an ER instead of FP. Set the ER recharge rate and conditions to work out to N uses per day.

To preserve as much of the original mechanic as possible, give each spell it's own, dedicated, ER. Not using one ability doesn't let you use another one more, so they can't share a common ER. This rates a hefty discount of the price of the ER. "One spell only" might well come in at -80%.

[sir_pudding]

What I intend to do if I ever do convert it, is just do the Dragonmarks as Magical Powers, concentrating more on the names and general effects rather than replicating D&D or GURPS spells exactly.

[Refplace]

Originally Posted by Raekai

Could you go into further detail? This sounds quite interesting.

Not sure I can say the specifics as I submitted it for a rejected Pyramid article several years ago and never got permission to do anything with it after that, though I asked. The concept however is widely used so no probelm going over that.

GURPS Divine Powers does something kind of similar though it has different appearance rolls on a patron as its core power design.
Lets say you build your core power as an Innate Attack with various enhancements and it costs 10 points per level.
then you can have a rank 1 to X with each rank being 10 points.
Rank 1 can let you buy a power that costs up to 10 points at 1/5 cost as an alternate ability. So each spell costs 1 or 2 points (10/5=2)
Rank 2 is 20 and each spell costs 11/5=2 to 20/5=4 points.
And so on.
the core power I used cost 40 points and had 5 Ranks for the epic level meaning a Rank 5 mage could buy spells up to 200 points (rank 5 *40=200) at 1/5 cost for say 40 points for a single very powerful Rank 5 spell.

Using Ranks like that even let you have a D&D kind of public power system such as Spell Levels.
You could use any power or set of powers as your base.
Telescopic Vision for a magic system based off Sight.
Mind Control for one based off mental powers.
Possibilities are endless.