Clerics of the Death Domain
Death is not a god. Death is the Grim Reaper who collects souls from the dying and takes them to its dominion on the moon Dora. There they await processing to their ultimate destinations in the Outer Planes.
Death is Neutral, but the Cult of Death is Evil, motivated by a desire to wield the power to snuff out lives. However, they are universally feared, hated and outlawed, to the point where there is no priesthood in the usual sense, only individual Clerics of the Death domain, scattered few and far between.
As Death only cares about reaping souls, Clerics of the Death domain may build great personal wealth by only ever sacrificing the living in exchange for spells. A black mass may only need a single Cleric and his sacrificial victim to be present. Death will always come to collect.