Walmart offers Just Dance 4 for Xbox 360 (pictured) or Nintendo Wii for $25. (Best Buy, Microsoft Store, and Amazon charge $25 with free shipping for the Xbox 360 version, while Amazon charges the same for Wii.) Opt for free Site-to-Store pickup to avoid the $1.97 shipping fee. That's the lowest total price we could find by at least $10. Sales tax is added where applicable.
Update: It's now out of stock or more expensive at Walmart, Best Buy, and Microsoft Store. Amazon still has the Xbox 360 version.