The component with the lowest price in the SEAT schematic is the Nut,flange,6mm.
Of all the components used in this assembly the Seat Comp,double is the most expensive.
Parts such as the Seat: Bolt,seat Lock, Nut,flange,6mm, Rubber,seat Mount, Stay,fr.seat are included in the Cx500 1980 (a) England Seat parts fiche.