A lot of the heated discussion took place after the Olympics. Following the games, prices have not materially changed and Beijing is back to its good old self (thank god for that).
Please I beg of you (if you find the thread, its around here and not too old) don't start another "How much to Mutianyu" thread.
My advice, if you have time and don't speak Mandarin, use the hotel doormen or concierge to write Mutianyu, for the day, round trip, and the price (let's say 300). Then bargain from there.