The Hut are selling "Yu-Gi-Oh! Tag Force 2" for the Sony PSP for £14.93 (inc Del.)
You can get cashback through the usual sites (e.g. 5% Quidco, making it just £14.18)
The next best price seems to be £17.95 from BlahDVD.
Enhanced "Tag Duel" System! Now up to 4 friends can duel at once!
Tons of new characters like Aster and Jesse! Who will you partner be!?
Now duel 2 vs 2 with your friends!
Includes 3 Limited Edition Official Game Cards Inside!