The Xbox 360 will be cheaper than Nintendo's Wii, but only in Japan. From Game|Life:
During a media event held in Tokyo today, Xbox Japan general manager Takashi Sensui announced price cuts for the Xbox 360 in Japan starting September 11. The bare-bones Arcade unit -- it comes with no hard drive -- will be priced at 19,800 yen ($183), making it the first current-gen console to dip under the $200 level. Nintendo's Wii is currently priced at 25,000 yen ($230) in Japan.
Microsoft Prices 360 Below $200 in Japan [Game|Life]