How about going oem and adding a CSS backbox? Seems popular and an econmical option.
I've been pricing this up over the last few days. Unfortunately the price has gone up by quite a bit from when I last thought about upgrading. VW want £597 and everywhere else is ~£100 less when you include the hidden postage. Was quoted £115 for postage from one eBay seller.
I called into Tony Banks exhaust in Leeds to enquire about a full system which came in at ~£1000.
The other option was to just change the tips to the same size as the Clubsport as I'm happy with how the stock system sounds, however I'm unsure on the diameter of the tips. This option is very cost effective at £40-50 each side.
I'd absolutely love to go with an Akrapovic system but I'm not sure I can justify spending £3,500 (before fitting) on an exhaust.