Extraordinary Trapsmith( Races of the Dragon, p. 100)
You are an expert at constructing mechanical traps.
Craft (trapmaking) 9 ranks,
When you determine the cost of raw materials and the time required to create a mechanical trap, reduce the base price by 25%.
A kobold who selects this feat can instead reduce the base price by 50% for determining raw materials and time required to create a mechanical trap.