The only things I've found so far on the nintendo store are Wiimotes and nunchucks, nothing else. I do remember someone saying they were only $10, though.
im personally surprised that its this cheap considering its integral to the functioning of the console...usually companies rape you for something you absolutely need
You can just use 2 candles or a powerful flashlight or anything that emits IR. It won't be long until 3rd parties release cheap ones that are battery powered (the only reason it's wired to the Wii is for power).
Candles work unreliably. And you'd have to keep lighting the candles every time you play. AND you'd have to replace the candles every so often, which will be well over $10 over the life of your Wii.