Parts such as the Valve / Rocker Arm: Cotter, Valve, Shaft,rocker Arm, Screw,tapet, Valve,inlet are included in the Cb500k2 Four 1973 Usa Valve / Rocker Arm parts fiche.
The component with the lowest price in the VALVE / ROCKER ARM schematic is the Nut, Tappet.
Of all the components used in this assembly the Valve,exhaust is the most expensive.