When I was flipping through the sale ads, I noticed that Best Buy has the Biggest Loser for the Wii discounted to $19.99 HERE. This is normally $39.99!
You can choose in-store pick-up to save on shipping charges. If you want to avoid the craziness of the stores or the gas costs to get there, shipping will cost around $2.99.
Just thought I'd pass it along in case any of you were waiting for a good deal on it. It's the cheapest I've seen so far.
UPDATE: It looks like Meijer and Target may have it for the same price this week. So you may want to call ahead and check.