The Hut are selling "Custom Robo Arena" for the Nintendo DS for £7.93 (inc Del.)
You can get cashback through the usual sites (e.g. 5% Quidco, making it just £7.53)
The next best price seems to be £12.49 from SoftUK.
Fight your way to the Custom Robo championship by combining hundreds of unique parts into the perfect fighting machine!
Go head-to-head over DS Wireless Communications or Nintendo Wi-Fi Connection, and pit your robo against your friends and rivals.
Explore a vast futuristic city and discover the world of Custom Robo as you battle your way to the Robo Cup!