Vindicator's Pendant of Dominance

Vindicator's Pendant of Dominance was a caster necklace introduced with Arena Season 3 to replace Veteran's Pendant of Dominance and Pendant of Dominance both of which are no longer available for purchase.

Source
The cost is and is available from these PvP vendors:
 * Champions' Hall, Stormwind
 * Hall of Legends, Orgrimmar