Thats like saying the 5770 will drop because the 5850 came out. The 69xx cards shouldn't cause the 68xx cards to change in price at all. They are to compete in different price brackets. You'd need Nvidia to change the price of the cards which the 6870 competes with. (GTX460)
If you don't want to buy the 6870, you can consider the 5830, 5850, and GTX460 or 470.