Our group has 5 19th century boxcar (and several flatcars and three passenger cars)
We just completed a complete restoration of a 1880 boxcar (as it appeared in 1899) including new trucks and link and pin couplers.
We are currently restoring a second 1880 boxcar (this time to its 1947 appearance)
We are in the middle of planning the restoration of a 1874 boxcar to its as built appearance.
Based on that experience, the cost of restoring such a car is about $85,000, for the materials only.
As it sits it is a shed with an interesting history. As a shed it is worth at most $1,000
As a boxcar it is worthless (that is what BNSF would offer) As a historic car it is priceless.
The true value is somewhere in the middle.
Randy Hees