I know this is a bit of a niche item, but I have been looking for one of these for some time and am trying to avoid paying the £88 dealers' price.
I found this one at Accessory Plus for almost £15 cheaper than the SEAT dealers prices. £6 for delivery, or free collection at your nearest Stoneacre auto dealers
There is some debate around compatibility with iPhone 4, but the general consensus is that it is compatible, although SEAT state that it is not. (http://www.seatcupra.net/forums/showthread.php?t=302252)
Edit - the link seems to have stopped working - copy & paste the link below:http://www.accessoryplus.co.uk/product/Ipod_Cable_and_Crable_1P9051785B