HMV is selling "Thrillville" for the Sony PS2 for £4.99 (inc Del.)
You can get cashback through the usual sites (e.g. 5% Quidco, making it just £4.74)
The next best price seems to be £12.99 from SoftUK.
Visit 'Thrillville' and step into a non-stop party in a theme park that you create. Customize your park, interact with guests like never before, and build and hop into your own roller coasters and other rides. For the first time ever race on go-kart tracks you construct, play mini-golf on courses you design, and more. Join friends for dozens of four-player party games, from bumper cars to arcade shoot-'em-ups. You can also tour the park on foot a first for theme-park titles chatting and joking with all the guests, helping them out and making sure they're enjoying themselves.
'Thrillville' combines elements of simulation, party games and social interaction like nothing before it, all in one of the most console-friendly theme park titles ever to be released. Its charming, laugh-out-loud story centres around you and the theme park you've inherited from your eccentric Uncle Mortimer. Only by keeping your guests happy and by completing most of the many missions on offer can you stave off the threat posed by the nefarious Globo-Joy corporation.