RV means relative value. As such, when Albert wrote his book, I have the bicentennial edition, a standard Union infantry general service button, the one with the eagle and no letters in the shield has an RV of 1. So...extrapolating, if one of those was worth $1.00 in 1976, then yours in good shape would be $15. So...today an eagle button like I described is average of $8. So yours would be 8 x $15 for comparison purposes.
As has been said, beauty is in the eye of the beholder, so it also depends on what market exists now for them. That's a very nice button. Congrats. We don't get many from that period where I am, not far away some are found, but most of that area is built up now.