So this helmet is what they call an Aviator style helmet. See link below:
http://www.antiquefootball.com/rarest_helmets.htm
It is a Reach Model 0 that was manufactured between 1900 - 1920.
It has some condition issues, especially the outside of one of the earflaps.
My best guess is that the helmet, in that condition would be about a $400 - $450 helmet.