What is a 1999 gold eagle 50 dollar coin mint worth?

You have a 1 Troy Oz coin. This would be worth around $890 at the current price. The gold index went up $100 today, you may want to sell later, it may go up again. Also note, you can typically sell solid silver/gold coins at a premium because they are more desired by collectors and investors. You could easily get $890 + 8-10% extra for this. Sell this for no less than $1000.