While historical, those old blue/yellow box RB drive Athearn's aren't really valuable or desired by today's crowd.
I see them for $10 at train shows, and see the same ones show after show.
Sorry.
If that really is a Varney steam loco, it's quite a bit more rare.
It's also NOT a "standard" Berkshire design.
Although Steam was almost always custom designed by a specific railroad in conjunction with a builder, most 2-8-4's were built late enough to be partially standardized to Lima's "Van Swearingen" design, which is quite a bit larger than the model represented above.
What road name is on the tender?
My bet on that one is AHM. If it had really deep wheel flanges, I'd say Rivarossi.