New in grease, with sling, unfired will bring a bit of a premium. Shoot it a few times and knock $50 off the price.
Most of the places that originally sold these beautiful rifles, took the wrapping off of them and sold the slings separately. If you can get one in the wrap includeing a sling, maybe as much as $450.
If its been shot, but still in excellent condition and no dings as well as cleaned properly, $300 is fair. Anything less is a very good deal. I would buy several right now for $250 each if they were still new in grease, with a sling and of course have been stored properly.
They are unapreciated, because they never saw combat in WWII and aren't Russian or Finn marked. They are also under valued in my estimation. Only time will tell. I kick myself for turning down good rifles because of a minor variation in settling price.