There's no reason to buy the 360 port, Ougon Musou Kyoku Cross is the last revision and it has more option, more character, new mechanics, etc.
It's not 100 dollars anywhere, Ougon Musou Kyoku and Ougon Musou Kyoku Cross (both for PC) are about 3000 yen (not sure how much in dollars, 'cause I'm european, but still under 50$), and the 360's port price dropped a lot in the last month, and I remember seein' it about 5000 yen.