Play are selling "MX vs ATV Untamed" for the Xbox 360 and Nintendo Wii for £24.99. Plus for the Nintendo DS for £14.99.
You can get cashback through the usual sites (e.g. 4% Quidco)
Next best prices: Xbox 360 = £29.98 (Amaxon) - Wii = £28.93 (The Hut) - DS = £16.99 (PowerPlay Direct)