Depending on the world I've had a few different ways to represent the cost of magic, varied by theme. Magic is Corrupting: What is says on the label. It's not a quick progression, but it's there. Every time a spell is cast the caster gains a number of points. Once those points reach X they get a minor problem (perhaps they become pallid, for a necromancer, or develop headaches). After that it increases in severity every X number of points. Note also that depending on the type of corruption there might be social repercussions involved. Magic is Painful: Once more, what it says on the label. Doing magic hurts. Either it's literal (the character experiences pain for a prolonged period, giving penalties to actions etc or they take damage, which will take time to heal) or it's figurative (as in their soul/mind is slowly burned, as per the style mentioned above, but with temporary problems such as Callous, Social Stigma or Confused). Magic is Expensive: Well, magic has a price and that price is paid in dollars. Materials cost a fortune and rightly so. Lower spells cost a fair bit, higher spells can only be cast by those with enough wealth or a willingness to steal. In a world like this the most feared mages would probably be CEOs or pop-stars. Magic brings the Wicked: And then we have one classic that I think is sadly under-used. When you use magic you light a torch in the darkness that guides only god knows what the way of the mage. Perhaps they're creatures that feed of magic, or things that want to get through to our world (or back to theirs) through the workings of the mage... or simply by burrowing into his body and slithering inside his soul to eat their way through. Perhaps they're just crazy people out to kill anything magical for some reason. Have fun with it! Magic is Unreliable: Using magic to light a cigarette is about as clever as using a molotov cocktail for the same purpose. It could be done, and with enough practice it might even do the trick you need it to, but it would still be a sure sign of being off your rocker. Big time. Every time someone casts a spell roll a catastrophe die (or something similar) to decide whether something goes wrong. If it does, don't let the spell fail, let it do what it should have, but Add to it. The fire to light the cigarette spreads wildly out of control, the teleportation moves them where they should've been but somehow they're moving, fast, along the ground when they arrive, the spell to summon and control a ghast works just fine... except that the four other ghasts don't seem to actually be under the control of the mage... Those are just some examples/ideas for you, none of them really suitable for DnD/Pathfinder if you ask me but all of them having lots of potential for fun in one world or another. Another fun treat is to have two or more types of magic, each with it's own tradeoff(s). Gives the players reason to carefully consider what they learn, if any of it.