Question about retrofitting…

…of xenon headlights. I’ve already read that it works here in the forum. But are there also workshops that would build that up at all? (No, I can’t do it myself and I really don’t know anyone who could do it). Because there are considerably more and also much cheaper used TTs without xenon (at least that’s how it seems to me). How big would the price difference have to be, so that retrofitting would be worthwhile? Same question about Bose and/or CD changers (gave it even without Bose?). I mean, to have read somewhere that both would be very expensive. Thanks already!