Neither result is very good.
Why let the Kastoroff out of the contract? He is responsible for the mistake and, in this sense, the cause of the waste that would be incurred from letting him out.
Why should the district have to bear this loss? Similarly, why should the district have to incur the costs and inconvenience of negotiating a new contract with the same contractor?
Between the contractor and the school district, it is fairer to impose the loss on the Kastoroff.
In this case, enforceable would not be unconscionable.