The component with the lowest price in the SWING ARM/CHAIN CASE schematic is the Nut,hex.,8mm.
Some items from this specific schematic: Slider,chain, Mark,(caution) Dr, Washer,swing Arm, Nut,hex 8mm.
With a quantity of four pieces, the Screw,flat,5x4.5 is the most used part in the SWING ARM/CHAIN CASE diagram.