Shotguns are normally referred to by gauge, not calbier. 28 gauge is .55 inches.
Suggested value is from $50 to $150.
50-400 usd
50-126
It depends. A box of 10 .50 BMG cartridges are something like $25 or $30. .50 AE is much cheaper. There are also other types of 50 caliber ammo and bullets.
50-100
You do not mention if it is a shotgun or rifle nor the gauge/caliber. Without a description of all features, markings, etc. there is no way to reliably value it. You could be in the 50 - 500 USD range give or take.
50-150 dollars is the going price for a Noble shotgun.
50-100 USD
50-100
50-125
50-500 usd
50-100