That is based on what? I doubt kickbacks exceed 10 percent. Remember there are other companies competing for the same contract - so kenya corruption is not monopoly - there is a thriving kickback market as each chinese or foreign company employs their own fatcat - and still have to compete on technical and commercial terms.
Once you have issued a contract with international companies - you simply have to see it through - or be prepared to pay heavy fines Moi era style.
If anything there should have been some arbitration - you dont just wake up like Uhuru did - drive to JKIA - and order chinese out.
Cutting losses
Once completed their premium above the real cost will be twice the 17B