These keys are quite common. A lot of people must have visited Master’s booth at the World’s Fair and taken one. I have seen them appear on eBay quite frequently, in condition ranging from tarnished and/or worn to pristine. I’m told by a certain long-time Master Lock collector that the keys were made for the public in both silver-colored and gold-colored versions, and that solid sterling silver ones were made for the “top officials”. As to the selling price, it can vary. I’ve seen pristine example(s) sell for less than $10 and others sell for over $20, maybe even over $30. I do not have one of these keys yet, but one of these days I’ll spring for a pristine one if I don’t have to pay much.
Zachary.