Average expenditure curve-Supply curve representing the price per unit that a firm pays for a good. Marginal expenditure curve-Curve describing the incremental cost of purchasing one additional unit of a good. In a competitive factor market,Profit maximization requires that marginal revenue product be equal to marginal expenditure: ME=MRP and that the price of the input is equal to marginal expenditure: ME=  Average expenditure curve - Supply curve representing the price per unit that a firm pays for a good.  Marginal expenditure curve - Curve describing the incremental cost of purchasing one additional unit of a good.  In a competitive factor market, Profit maximization requires that marginal revenue product be equal to marginal expenditure: ME = MRP and that the price of the input is equal to marginal expenditure: ME = 