I like creating various magic systems, but keeping it simple can be challanging.
The idea I have is for exponential power costs for spells that can take days to recover from using high level spells yet allow nearly limitless use of cantrips and such.
Basically, run on spellpoints and treat the spell level as the exponent for how much mana it takes to cast the spell. So sl 0 costs 1 point, sl 1 costs 10 points, sl 2 costs 100 points,... sl 9 costs 1 billion points.
I like what the concept represents, but using it directly like this would be quite ridiculous and painful to track.
One of the aspects here though is to allow the lowest level spells to be used freely without worry about the cost, but as the sl goes up, it becomes an increasing problem. I also want low to mid spells to be recovered from quickly to perhaps a day, but have higher spells take days to a week to recover from, and the closer to empty the caster runs, the more difficult it becomes to cast any spell.
Of course, getting multiple casters together to cast a spell to spread the cost among them should be viable but this also raises how powerful of a spell that can be cast.
And of course, I want the difficulty of casting to be separate from the mana cost. (will be using some form of casting check to determine the effectiveness of the spell)
So I'm hoping some of you can help me figure out a way to represent this without trying to keep track of millions of spell points.