In any or all of the above cases where local units of government are required to pay or participate in the cost of right-of-way and such right-of-way cannot be secured by negotiation, the state and the local units of government involved shall agree upon a fair and reasonable offer to be made for the right-of-way and, should the eventual cost thereof exceed the offer, the excess shall be borne with the local units of government involved, in proportion to their respective obligations in the purchase of such right-of-way, and shall be computed on the basis of each tract separately.
Okla. Stat. tit. 69, § 1206