I've been trying to look at the the trade-in tracker to see how much trade-in values these have at Gamestop, but it seems to not be working. But the Wii version is at $13.00 on Amazon. Selling the game for $15.56 brand new and buying it back used for $13. Something tells me one of those will change in the near future. Normally I'd buy the 360 version, but its value is only $8.75 at Amazon. Hmm...
Edit: It appears to be part of the "Wii price drop event" sale due to the Wii lowering in price, and will be back up to regular price on the 21st. We can probably assume the same for the other versions.