u/ChocolateAlarmed9090

I live in Brazil. In 2023/24, I saw on a website that a 1964 half-dollar coin was auctioned for $18,000, but I see that its value on eBay is far from that. I have one that I received as a souvenir from a US diplomatic corps employee. Can anyone give me an idea of ​​the value of this piece? It has never circulated, it's just dirty from age.