Generally, such prices appear when two auctioners really want the item. If such another shoulder straps is offered in auction, I guess the final price would be lower.
Here is another example of a reservist from RJR82, from a man who has been prisonner during the battle of Ourcq at the begin of september 1914. Still no reserve Kreuz and the troop Land cocarde.
It belongs to Vize Feldwebel Hattenhauer, wounded on the 20th Septembre 1914 near Soissons and dead in a hospital on the 28th October in Namur. Your helmet might come from the same battle, whre lots of men of RJR 66 were killed ou made prisonner or from the battle of the Ourcq beginning...