I am trying to make a educated guess, and I say within 3 months. It will be cheaper than what you have on your list and you can unlock the pipelines on it and OC it to the speed of GTX.
its going to be 250 if its more then you could just get a 7800GT if it less then that wuold be good cause the 6800GS are about 50-100 dollars below the 6800GT so the 7800GS would most likley be 50-100 dollars less so 200-250 im guessing