An all Rosewood or Ebony neck ain't exactly on the cheap. And like the Wenge idea that was nixxed because of of orange streaks (that I've never seen), Rosewood and Ebony (the non-Jet Black variety) can have have orange and brown streaks too.
I know you were wanting to go exotic, but how about a Maple or Mahogany neck with the back and headstock paint matched to the body with an exotic fretboard. And if ordering the body already finished from the showcase, they are hesitant to match a neck after the fact, get a neon purple painted neck. Sure it's weird, but......