The Collet is the cheapest item from this partsfiche.
Parts such as the Valve(s): Shim,t=3.10, Shim,t=3.40, Shim,t=3.15, Shim,t=3.20 are included in the Zr900bhf Z900 2017 Europe,middle East,africa Valve(s) parts fiche.
The Valve(s) assembly is constructed from several parts from which the Valve-exhaust is the most expensive.