According to Andrew Leman, member of the H.P. Lovecraft Historical Society, they have an idea on how to adapt At the Mountains of Madness for the big screen.
"We’ve occasionally said to people who know Guillermo," Leman shared, "that if you’re done with that story, we’ll happily take At The Mountains of Madness off your hands. We have an idea for doing it that would cost much less than $250 million."
Source:
Why Arent There More Lovecraft Films? | Nerdist.