Both smiths (Geoff in Ars Magicana and Grisha in the dwarven halls) tend to have a lot of money. The amount of money merchants have is determined when their inventories get re-set periodically (about 10-15 minutes real time after last talking to, hitting alt near, or running your cursor over them). Unless they start holding on to a lot of the stuff you sell them (which get listed above the gold and randomized inventory) their gold keeps replenishing within about the same amount range.
