Game are selling "Chronos Twin" for the Nintendo DS for £7.99 (inc Del.)
You can get cashback through the usual sites (e.g. 11% Quidco, making it just £7.11)
The next best in-stock price seems to be £12.99 from Gameplay.
Chronos Twin plays on the concept of time travel in a reassuringly unique manner as it is interwoven as a main game play element. To successfully complete levels, players will maneuver through an area and work within the limitations of each time period in a side-scrolling environment. The goal is to control both the present-time hero while exploring the planet to defeat alien threats. Both time periods are fully visible through a split-screen engine that displays the past and present versions of the exact same location.