The Keynesian range of aggregate supply corresponds to the proposition that when price are very low, firms will prefer to cut production rather than sell at a loss. In this range, any change in aggregate demand will produce a change in output. Thus, in the case of a recession the correct government policy is to expand aggregate demand.
Numerous sectors of the economy have very few changes in price but sizable changes in the volume of production and the number of employees. For example, car manufacturers offer rebates which do not amount to even 10% of the value of a car. Compared to changes in price of 50% or more in clothing for instance, the car rebates are very small. The reason is the large fixed costs. Closings of entire car manufacturing plants are not uncommon during recessions.