It's definately fairly rare. I can't find any mintage numbers but I've seen the 20 oz exact same design listed and they had a mintage of under 3k. You won't see many with that stamp because most have been melted down over the years. I honestly wouldn't pay too much over spot tho because it's a niche market for bars like that. If it were at my coin shop I wouldn't pay much over spot for it and if I were to sell it I wouldn't get any premium for it at all even tho it's so old. Items like this you have to sell online. Now if you can get it for a decent price I'd turn right around and list it for a rediculous price on eBay and hope to hook someone for a couple hundred over spot..