How about commoners

In economics 101, if the demand is high, and supply is low, then people will buy it for that (inflated) price.
If the supply is high, and demand is high/low, then people will shop around for the better deal (either price or quality).

But the noble people here are planting their own garden of potatoes for the flowers, which nullifies the need to purchase the farmers' already grown potatoes, effectively prevents the rise in price for the farmers' potatoes. - The nobles want the flowers, not the food.