MTG Salvation

If I have a Volrath's Curse on my creature, can I use it as a repeatable sacrifice outlet or can I only "ignore this effect" once per turn?

No. Since the effect does not use the stack, there is nothing to respond to once the creature is sacrificed. This means the "ignore this effect" clause is now active. The effect you are ignoring is the entire effect. That means there is now nothing allowing you to sacrifice a creature because the effect that was letting you do that is now being ignored.