From what I can tell, at least with the divine reagent vendors, they give you a discount of about 15-17.5%. However, they're really not that useful - They only offer the standard reagents, which are cheap as hell anyway, and by 'divine' they mean 'cleric' - Rangers and paladins still need to go somewhere else to buy their stuff. I'd recommend you add the special reagents needed for specific spells, since that's what people would want and expect, and you include all divine classes (Ranger, Paladin, Cleric, FvS, Druid eventually) with the divine vendor and all arcane classes (Wiz, Sorc, Bard) with the arcane vendor, to make these vendors something people might actually use. As it is, saving five hundred plat on a purchase of 1000 ninth-level spell components that you'll probably make once every two months is just giving the illusion of a bonus.