B>Jett Permanent NX Cape

The cape seems to only come from the boxes you get from Maple Admin by turning in outfits and getting cupouns to exchange for the special box, and the rate of permanet stuff from them is low. I doubt you would find any at the price you suggest.
You could always wait for the magic anvil and use it on your "endgame" cape together with the cape you get from the start as a Jett, seeing as it is identical.

He might be after the set effect animation though.