Where an existing timber sale contract between the Secretary of Agriculture or the Secretary of the Interior and a timber purchaser does not provide relief from major physical change not due to negligence of the purchaser prior to approval of construction of any section of specified road or of any other specified development facility and, as a result of a major disaster, a major physical change results in additional construction work in connection with such road or facility by such purchaser with an estimated cost, as determined by the appropriate Secretary, (1) of more than $1,000 for sales under one million board feet, (2) of more than $1 per thousand board feet for sales of one to three million board feet, or (3) of more than $3,000 for sales over three million board feet, such increased construction cost shall be borne by the United States.