[PvK]

Well, see the Price of Power mod I just posted for another idea.

There are various other ways magic can be limited. For example, any number of spells can be made national. Players could do a picking process where they choose which spells they want to have in sequence, for the top however-many spells. Or an auction process where the highest bidder by cost/requirements gets the spell for their nation at that cost. e.g. "I claim Wish at 300 pearls as a N9 A9 spell".