The component with the lowest price in the VALVE - UPPER ROCKER ARM schematic is the Nut, Tappet Adjg..
Parts such as the Valve - Upper Rocker Arm: Arm A.up Rocker, Seat,spring, Shaft.up Rockearm, Cotter, Valve are included in the Cx500c Custom 1981 (b) European Direct Sales Valve - Upper Rocker Arm parts fiche.
Of all the components used in this assembly the Arm B,up Rocker is the most expensive.