The official line from Nintendo is that the Wii Wheel steering wheel accessory will be available in the beginning of 2008, along with the Wii version of Mario Kart. However, I just got back from Europe, where I happened to spot that very product for sale in an electronics store within the Amsterdam airport for 20 Euros, or about $26. Check it out.
And if your first thought is “Oh, it’s a third-party knock-off”, then I ask you to check out the official-(looking) Nintendo logos on the bottom corners of the box. They don’t do it like that on Canal Street.