Demand is not dictated by the cost of production. They are not the only AC manufacturer. Let me help you. If China canceled 400 orders Boeing would have over capacity of production. This would cause Boeing to either lower there price, reduce profit margins, or close down some production. It would not cause a price increase. That would be suicidal. If an airline is deciding on new equipment it comes down to a few pennies on the dollar to make a decision. It isn’t a massive cost reduction just enough to make them choose Boeing.
Let me help you. If Boeing had to pay for their new aircraft plant with 100 planes, instead of 500 planes, would their fixed cost per plane be higher or lower?