The Nut,flange,5mm is the cheapest item from this partsfiche.
Parts such as the Rear Fender: Cap,rear Bumper, Collar B,rr.fend., Fender A,rear, Nut,flange,5mm are included in the Cb450s 1986 (g) Germany / 27p Rear Fender parts fiche.
Of all the components used in this assembly the Fender A,rear is the most expensive.