It's speculated that the GeForce GTX 880 will feature a 256-bit memory bus and may be launched with 4GB GDDR5. The launch price is expected to be in the $400 to $450 range, it's not finalized yet but $500 is said to be unlikely.
One important thing to note though is that the GeForce GTX 880 is based on the GK104 GPU and will not deliver a new lever of performance. Not a lot of has leaked out about the performance level of the card but educated guesses put it between the GeForce GTX 780 and the GeForce GTX 780 Ti.
GeForce GTX 880 might not be the fastest card out there, but it will not hurt your wallet — $400 – $450 is expected MSRP. Of course it is yet too soon to confirm the price, but it is unlikely that GTX 880 will cost $500. From manufacturers perspective, GeForce GTX 880 is using very similar board design to GTX 770. GeForce GTX 880 is of course 780 successor, but it has more similarities to GTX 770 than GTX 780.
The difference between GTX 880 and GTX 770 boards is cosmetic. Thus, GM204 is basically a GK104 replacement. However, just because it’s a mid-range GPU replacement, It does not mean it will be slower than some GK110 cards. We do not know how fast GTX 880 is going to be, but it’s safe to assume it will sit above 780 and maybe even 780 Ti.