There are fixed costs associated with any manufacturing process whether you are building one piece of a design or thousands.   When a large quantity of an item is being ordered, the fixed costs are distributed over many units and as a result of the large quantity, can be included in the unit cost. If a small quantity of an item is ordered the manufacturing fixed costs represent a more significant percentage of the overall cost. 

A Low Volume Charge (LVC) is quoted as a separate amount for each custom potentiometers design when ordered in quantity under 25 pieces.