In my game I keep it simple. I remove the component cost for effects that duplicate 8th level spells and under. 25,000 for an Invisibility spell or the like cause you have a wish you havent used but need a much lower power spell you don't currently have access to is too much by far.
So duplicating spell effects 8th and below free just like the divine casters. Now if you want to never breathe again, grow wings permanently, increase a stat or the like, or to really test the GMs patience with something grander. 25,000 seems fine.
Just saying "Its a god granting the spell and a wizard isnt a god" doesnt quite cut it when either can cast a spell of 9th level which the game designers have stated clearly that they believe Wish and Miracle are THAT power level without divine intervention. The priest draws power from the outer planes, the mage from his own force of will, but they can , in EVERY SINGLE OTHER CASE, perform the same feats of magic at the same levels. There is no reason arcanes should get such a massive penalty to what can otherwise be a very handy spell.
either case. Reasonable power , reasonable cost. Major power, Major cost. Simple.