They cost peanuts!
I went into a VW parts garage(not main dealer) and bought one at a cost of 85p but they stupidly gave me one box of four instead of just one...bonus
Also worth noting I got the oval twist type, earlier mk4 models had the round pop-in type.
And...(haha) they are really easy to change as the whole thing just screws in and out.
Hope this helps.