This article details Hârnic currencies, the operation of Royal Mints, Counterfeiting, Usury, the Lore skill of Numismatics, and 30 rare coins that might turn up in a character's purse.
The Keep on the Borderlands is set in Dyriamarch, a region of Melderyn claimed, but not effectively controlled by that kingdom. There is also a letter meant to be handed to the players before the adventure.