Well my character is pretty old and I'm considering bringing in an even older NPC for plot jazz. Though yours would be more 3-400, if we're talking Salem.
Here's kind of a problem I'm having, though. His price is reasonable, I think, really. But because it has such a long time span it really won't come into play during the game itself. That comes off as kind of unfair to me; every other player is going to be dealing with it throughout the RP, but you're pretty much safe from it. Even if it does come up, it'll only be the one time.
I like the vein it's in, though. A price of blood and fire, it works really well for a dragon based witch, I would just say that he should have to pay it more often, like monthly. In fact, I notice that both of the witches already made have monthly consequences tied to the moon.
EDIT: To be clear, I don't mean he should pay that exact price, but a lesser price more often, y'know?