Bladeforged make great challenge farmers, too! 1 paladin level, then 14 sorcerer levels for delayed blast fireball. Either run it like that or take 1 more paladin level for divine grace and sit at level 16 indefinitely. Big boost to challenge rewards when running at level 20. Requires virtually no gear -- tier 1 cloak of flames and rock boots from the same challenges and a decent thaumaturgy staff and you're ready to go.
But . . . I doubt anyone spent the money just to have an easy way to make a challenge farmer.