This is not official, but merely answers to the best of my knowledge.
Question: How much will it cost?
Answer: Nothing. If you own the game it will be free, though it will require you install patch 1.9 or later.
Question: How much will it hurt performance?
Answer: No one except Crytek employees will really know the answer to this until it is released. However, we can speculate! Feel free to share your thoughts below, but I'm expecting a 20%-50% hit to the frame rate with everything at max (assuming your videocard supports all the features). Why the big range? Simple: these features are extremely advanced, but the CryEngine3 and dx11 are both highly optimized (over CryEngine2 and dx9). It's anyone's guess as to how this will balance out in terms of performance. Feel free to share your expectations below!
Question: How much disk space will it eat up?
Answer: The dx11 part is around a half a gig, but the HQ texture pack is a bit more complicated. The download size is around 1.7gb, but this is a compressed file. Early reports indicate it will take up over 5gb once installed.
Question: Will there be new graphics options or will it override the current "Extreme" graphics settings?
Answer: It is very unlikely this will replace the Extreme presets. I've heard this referred to as the "Ultra Pack" by nVidia employees. So, odds are good there will be a new Ultra preset under graphics options to enable these advanced features. Additional graphics options will be available in the advanced graphics options menu as well, though it is unclear precisely which new elements will be adjustable.
If you have any additional questions, post them below. I'll do my best to find answers. Keep in mind that some of your questions may be answered in the official early patch notes or dx11 thread.
https://secure.gamesas.com/forums/viewtopic.php?f=40&t=32220
https://secure.gamesas.com/forums/viewtopic.php?f=40&t=32248