The 560ti was made to compete with the 6950 1GB, not the 6870. The 6950 prices are high because they have been discontinued and few to be found.
The 6950 is discontinued and replaced with the HD7850 2GB, which is a little high priced right now because it just came out. The 7850 is faster than the 560ti though.
I have a feeling we will see a 1GB version of the HD7850 soon at a lower price.