I have seen a few of the Bethesda Farm Dairy bottles around, but usually they are private mold rather than slug plate like this one. I have seen, if I recall correctly, 3 others like yours. I would say its a fairly scarce one.
Scarce typically = $$. Since I'm partial to Virginia & DC, I'd be willing to part with this one for the right price if you know anybody that would be interrested.