A potent spell that permanently destroys magic:

Dead Zone
Level: Magic 9, Sor/Wiz 9
Components: V,S,M, F
Casting Time: 1 hour
Range: Close (25 ft. + 5 ft./2 levels)
Area: 100ft cubed
Duration: Permanent
Saving Throw: No
Spell Resistance: No

This spell creates a permanent immobile cube shaped anti-magic field. A Dead Zone cannot be created in any area that contains an ongoing spell, magical creature, or magical object.

It is impossible to scry or teleport into a Dead Zone. A Mage's Disjunction has a small chance of destroying it, just as with a personal anti-magic field.

Creating a Dead Zone is risky for the caster. The caster must succeed on a DC30 Spellcraft check or permanently lose one level from their caster class and become unable to cast any spells for 1d6 days. Even if successful the caster temporarily loses a level for 7 days.

3000xp and bones of assorted magical animals worth 10,000gp.

A small cube of cold iron worth 100gp.