Gold Silver and Copper

A system that allows the Gold and Silver and Copper to be exchanged with a set of rules would be nice for instance 100 copper equals 1 Silver, 100 Silver equals 1 Gold, other wise Franz, does not know how to price items, and instead of pricing with one set, we could then use all three sets to price goods such as an item costing 5 Gold 10 Silver and 5 Copper.