who give them the price?
is there only one like it all over the world?
Prices for rare coins are set during auctions. You have to know what people are willing to bid before you set a price. As this coin has never been on an auction, it's hard to guess. But one can estimate. Other gold coins which only exist in one exemplar has been sold on auctions. It is not unlikely this one would be in that price range. Then we're talking about $10 000 000. Probably more as it was a few years since last time and because we tend to see new records each time something unique comes for sale.
Only one, yes. It's a US coin, no other country can make them. If they do, it's called forgeries. And forgeries are not valuable.
ST rank 5 (best 1) - 10 wins, 2 titles (Paris 2014, Madrid 2015)
vBookie net amount won: 47831 (2015: + 16661, 2014: +24475, 2013: +6795, 2012: -100)
TT singles rank 70 (high 52), Titles: Memphis 2015.... TT doubles rank 47 (high 40). Titles: Quito 2015 (w/scarecrows)
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