A few hundred to museum priceless depending on specifics
You will need a professional appraisal
It should be a #11 cap.
50-100 USD
50-100
50-200 USD
50-300
50-125 or so
Yes, I can. A Barrett M107 is a .50 caliber sniper rifle.
50-150
50-125 USD
50-2000 usd
50-500 USD or so