The cheapest price at the moment is £30 in game, play.com and amazon.
you could go there or you could go onto Ebay.com - it still has people trying to sell them at £30 but then it has some at like £10 - upwards. (be careful not to get the leaflet or the downlodes unless you mean to because it has people selling them on it too.)
Or if you want the cheapest Irish place, it's Argos for 37.99 Euro (On PC and Wii. The DS game is cheaper!)...
PC World has the dearest so far. 49.99 Euro!!
Definitely go to Argos!
Hope that's answered your question! X