$40 is correct (although I've seen $50, most sources say $40) Rebel Frau Eva, but you've missed the mark with the reason. The table on which the surrender terms were drawn was purchased for $25 by Gen. Sheridan and presented to Gen. Custer (for his wife).
But why $40? Hmmmmmn, Eva! You'll have to do better than that to help "The Cause"..........
"There are few subjects that ignite more casual, uninformed bigotry and condescension from elites in this nation more than Dixie - Jonah Goldberg"