ShopTo are selling "Pro Evolution Soccer 2008" for the Sony PSP for £12.99 (inc Del.)
You can get cashback through the usual sites (e.g. 4% Quidco, making it just £12.47).
The next best price seems to be £14.99 from ChoicesUK.
Key to PES 2008 is a proprietary adaptive AI system entitled Teamvision. Unique to the Konami game, Teamvision is a sophisticated AI programming that learns and adapts according to an individual's style of play. As such, it will learn new ways to build attacks and to counter specific movements and previous attacking or defensive errors, ensuring games are more in line with the tactical but flowing nature of the real thing.
With the Pro Evolution Soccer series renowned for its fluid, realistic gameplay, the new game builds on the implementation of Teamvision with additional key advances. As with previous releases since its inception in 1996, the ball is again treated as a separate entity, with the timing of shots entirely down to the player, while the new AI ensures that defenders work to close down space and block efforts on goal. Similarly, distribution of passes works along the same lines, with players using the space available to them to switch the ball. Close control has also been enhanced with more control when dribbling the ball, and a number of subtle moves added to bypass defenders and move the ball into space.
Working in conjunction with the Teamvision system, every aspect of Pro Evolution Soccer 2008's on-field play has been reworked and fine-tuned to create the balanced and strategic play of a high stakes match. Set-pieces have been improved, with full control given over the number of players and the position of the defensive wall. A wider range of set piece options are also available to make use of specific talents within the team.
'Next Generation' versions of Pro Evolution Soccer 2008's are further enhanced by stunning aesthetic elements. Player detail has been taken to incredible levels with full facial animation and the high-definition detail afforded by the hardware used to show full movement and subtle details to the various kits during the course of a match. All 'Next Gen' versions will also benefit from an extensive Edit mode.