Phoronix article: https://www.phoronix.com/news/Steam-Machines-Frame-2026
Also listed here: https://store.steampowered.com/sale/hardware
Valve has already sent support for the new Steam Controller upstream: https://www.phoronix.com/news/New-Steam-Controller-SDL
Valve engineers told GamersNexus that it should be priced no more than the index, but they did not specify which kit or package of the index. So yeah, anywhere from 700 to 900 dollars probably.