I did the polo rear aero arm - makes the back look MUCH tidier mate, well worth doing it.
I found one on ebay for £18 delivered.... not sure how much they are from stealers though..... as macdaddy said, you need to trim the cap slightly so it sits right and the wiper is still functional, but its well easy - even I could do it and Im useless.
WOW - that's kinda priceee. You should just buy it at a German dealership for 26euro on your way to Nurburgring!
I can recommend my dealership in Wittlich - they've always helped me look for parts, and some of them speak english. Or the dealer in Bitburg is close-by/good too, and ALL of those guys speak engarish.