This WeakAura is a continuation from https://wago.io/VqDulG65P, I've updated it for Wrath and expanded the custom options to Death Knight, Druid, Hunter, Mage, Paladin, Priest, Shaman and Warlock. Set howmuch of the Reagent you want to auto buy in the custom options tab.
For Hunters this WeakAura auto refills the current ammo that you have in your ammo bag.