Xtendplay is currently £12.95 at Limexb360 on both Playstation and Xbox
http://www.limexb360.co.uk/product/XtendPlay_for_Xbox_360_XTPLXB
However, the same company appears to have an ebay seller account, and are selling exactly the same product at £9.99, which includes postage.
http://www.ebay.co.uk/itm/XtendPlay-Controller-Add-on-Xbox360-/270921944232?pt=UK_Controllers_Attachments&hash=item3f1434cca8#ht_788wt_956
http://www.limexb360.co.uk/product/XtendPlay_for_Xbox_360_XTPLXB
However, the same company appears to have an ebay seller account, and are selling exactly the same product at £9.99, which includes postage.
http://www.ebay.co.uk/itm/XtendPlay-Controller-Add-on-Xbox360-/270921944232?pt=UK_Controllers_Attachments&hash=item3f1434cca8#ht_788wt_956