Any character who can hit AC 23 can kill him on a 21,000 gp budget.
Why, Because 20,000 gp of holy water and some dust of dryness (850 gp) makes a holy hand grenade that deals 1600d4 damage (average 4000).
a 8th level wizard has enough money, an could use true strike and launch item. Hell, the wizard only need survive one turn within 180+move speed of the guy before killing him. With a level 0 spell.
Sure it would take 3/4 of his WBL, but it's to one-shot kill something CR 50.