Just spoke to my local VW Parts Dept for a price on the TCR Backbox and diffusor, honestly can't believe how much more expensive the TCR backbox is over my previous CSS blackbox.
£716 was the best price they could offer for the backbox, I paid about £500 - £600 for the CSS which included fitting!
Diffusor came in at £170 + £12ea for the corner bits. Just incase that's useful information for anyone looking at picking those bits up.