(1) If the contract is based on a cost estimate without the contractor guaranteeing the accuracy of the estimate and if it becomes apparent that the work cannot be carried out without substantially exceeding the estimate, then, if the customer terminates the contract for this reason, the contractor will be entitled only to the claim specified in section 645 (1).
(2) If such exceeding of the estimate is to be expected, then the contractor is to notify the customer without undue delay.