20 usd? i dont really know...

In perfect conditions, I'd say 35 (I'm talking about the new version with the motion plus included)

For third partie ones, I'd pay about 15. For good condition regular ones, 20, and for plus ones, 30.

Last year I got an official used Wii mote with motion plus for around 20-25€, so probably that. (And it works pretty well!) But if you want a brand new one, then I'm pretty sure you can find one for 30-35