According to the rules, each gold piece weighs 1/50 of a pound. A little conversion, and we have a weight of 0.291667 troy ounces. Therefore, at Friday's close of $689.70 per troy ounce, a gold piece is worth about US$201.16.
A Ring of Djinni Calling has a market value of 125,000gp. Using the above values, we come up with an equivalent price of US$25,145,312.50.
So all you have to do is give him the above price as a ballpark, and tell him that the final price would depend on the current value of gold. Also tell him that supplies are extremely limited. If he does place an order, tell him you are currently out of stock, with no estimate on a restock date.
