The Bulb, Taillight (12v 21/5w) is the cheapest item from this partsfiche.
In this schematic the "Bulb, Taillight (12v 21/5w)" is used most often.
Parts such as the Taillight: Pad, Washer, Plate, Grommet (4l0), Support, Tail Cover are included in the Yzf1000r 2000 4sv5 England 104sv-300e2 Taillight parts fiche.