One thing I would change about that gauntlet is using Prismatic Ray from Spell Compendium as base spell for creating the item instead of Prismatic Spray. All of the effects it produces are exactly the same, except that the spell is a level lower which will drop the cost. The spell also produces a single-target ray (ranged touch attack + saving throw) instead of a cone, which more closely resembles the functionality of the gauntlet, and could justify tripling the range of the gauntlet's abilities.