The component with the lowest price in the F-13 SEAT schematic is the Bolt,flange, 8x20.
Parts such as the F-13 Seat: Rubber,seat, Bolt,flange 6x10, Cushion A,seat, Bolt,special,6mm are included in the Xr500 1980 (a) Canada F-13 Seat parts fiche.
Check out any of the nine F-13 Seat components enlisted.