Not so sure how much leverage they have regarding Courtois. Atletico can say "take your goalie", and then what will Chelsea do? They can't keep both Courtois and Cech.
Chelsea are in a tricky place, but I am confident that they will raise the required funds to put in a massive bid for Costa and then deal with the clean-up afterwards. That could mean selling Will.I.An, Schurrle, Ba, Torres, Lukaku, whoever. They'll deal with it afterwards