It will depend on the condition. Antique firearms are rare enough that it will be hard to name a "book value" sight unseen. You will need a "hands on" appraisal.
50-100 or so
what is the value of a 1945 single shot 22
50.00 dollars
50-300
Which model?
Impossible to answer without knowing if it is a rifle or shotgun.
25-100 USD, 12 gauge is a shotgun, not a rifle.
its value is what another man is willing to pay for it.
200
25-100 or so
100-1000 USD or so
Blue Book of Gun Values will help.