New Super Mario Bros. U for the Wii U
Delivery free if over £20, cheapest item I can find to add is "Angry Birds" for the PC (£1.97).
Although there were some 19.99 deals over the past month these seem to have expired.
Gamestop also have Nintendo Land for £12.97 which again seems a good price. However you need to hit that £20 free delivery mark to make the most of this.
Hope this helps someone :)