As with any firearm, it is not possible to accurately appraise a gun without seeing it. Recommend that you see a local gun dealer for an appraisal. You can also do your own investigation by looking at other models being sold that are in the same condition as yours. Try the gunbroker.com or a periodical called "The Gun List" You can also reference the Blue Book of Gun Values which can be purchased on line at various retailers.
Yes, Browning made the B80.
100-400 USD
50-500 usd
Depending on condition, from 250-450 USD.
$250-500 depending on condition
1981
Download a manual from Browning or take it to a gunsmith
Best left to a gunsmith
Your Browning B-80 in the description you described is valued at 450 dollars.
Best to ask a gunsmith for help.
$250-500 depending on condition
You need to see a gunsmith.