How is much is an E-Plurimbus Unum coin with a moon in the background worth that has an FG between the eagle's left foot and the branch it's carrying?

From your description the coin is a common Susan B. Anthony dollar (1979-1981 & 1999) that is in circulation today. The FG is the designers monogram and adds nothing to the value of the coin. It's just a dollar coin, spend it.