Be aware that the chambering is most likely 12/65, not the 12/70 common today (it should be marked with 70 if it were). While the 12/70 might fit they are not a good diet for the gun. 8x57 IRS is a great elk and boar cartridge, and is sold in a Sellier&Bellot (Check made) load typically for less than $ 20 per 20 in the US.
I agree with the valuation, somewhere in the $1000 to 1500 range. It could use a good restorative cleaning (hunting guns are less critical to keep in "as made" condition), and as JK said without a marker's name it is only its current state that counts.
I used to love being able to hit hard at 1000 yards. As I get older I find hitting a mini ram at 200 yards with the 22 oddly more satisfying.