Values can vary allot as the depth of buyers pockets do and can vary, its all dependant of the condition of the rifle in general with the bore being top of the list.
Not sure on what year they went away from mercuric primers but they were very bad for the bores forming salts and rusting bores in a matter of hours after use or battle.

They range here from $500 - $600 Aud for a well used one to $1,000 + for a really top notch one again the market decides pretty much the top prices, again asking and getting are two different things I have seen high priced ones still for sale after 12 months listed.