"Laws often include exceptions for price increases that can be justified in terms of the increased cost of supply, transportation, demand, or storage."

IANL Based on the above definition, it sounds like OP is not describing price gouging. Their business is not setting the price of the goods directly. The buyers are competing for a limited supply and pushing each other to bid higher amounts. That sounds like a justifiable increase.

Now, if the mill saw the emergency and said "we won't take less than cost + 45% ..." or something like that, it would likely fall into price gouging territory.