The liner looks good and original to the helmet. The shell was made by BXF Westfälische Aluminiumindustrie Jürger & Co, and there may be a stamp on the liner from a manufacturer as well. It's a pre-war police helmet, not in the best condition with the chinstrap and decals gone, plus pretty heavy paint wear, but still a nice example.
These "civil" helmets, made of aluminum were never intended for combat, but by wars end, the Volkssturm was using whatever they could get ahold of, so who knows what your helmet may have seen.... I like it, I've been keeping an eye out for helmets lately and I'd be happy to find one like it.
As to value... taking into account the condition issues, the paint wear, no decals, no chinstrap, the leather tabs that would have held a removable leather flap on the back for extra neck protection.... $75 - $100.00 or thereabouts would be fair I think, they just don't get the prices combat helmets get, even though I saw some online with asking prices that were really optimistic, to put it kindly.
Whatever the case, it's a cool helmet, and a great find
