Can't see a GTI one on their site, just the soot chucker VOTEX version without a zorst cut out, sure they used to sell them, ho hum!
From America the OEM GTI ones are around £350 before import taxes (if you can even find a company that will ship, I know ESC Tuning won't), handling and a painting so not cheap.
Couple of soot chucker ones on eBay, just type in "Mk5 golf bumper" and you'll see them. A good bodyshop should be able to cut out a zorst exit and make good for a reasonable price., might be your best bet.