Yes, welcome to Tnet.
George F. Cram was in partnership with Rufus Blanchard from 1867 but Cram took full control of the business in 1869, at which time he renamed it as the “George F. Cram” company.
Lots of other dating clues such as: the “Dominion of Canada” didn’t exist under that name until 1867, and the “Indian Territory” shown had already been eroded by 1890 before it ceased to exist in 1907 when it was annexed to become Oklahoma. More specifically, Dakota is shown as a single territory (ie pre-1899) with borders consistent with post-1869, but missing the small Niobrara River area that was transferred to Nebraska in 1882.
So, you could put it somewhere between 1869 and 1881. These kinds of maps had large print runs and, without any special interest such as railroads or whatever, I doubt that it would fetch more than about $15.