As with any firearm, it is not possible to accurately appraise a gun without seeing it. Condition, and original configuration will determine value. Other factors such as rarity of caliber or guage and higher grades have significant impact on value. 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.
Download a manual from Browning or take it to a gunsmith
Yes, Browning made the B80.
100-400 USD
50-500 usd
Not sure if it is a B80 or an A500, but it was made in 1988 in Europe (not Japan). Depending on which model, $400-$500.
1985
Several, the auto5, B2000, B80 and others
Depending on condition, from 250-450 USD.
$250-500 depending on condition
1981
Is it a Browning? If so,is it a BPS,B80,A500,Double Auto,Auto5,Gold,A-Bolt,O/U or SxS? What gauge? Your question is sort of like asking, "I have a truck. What is it worth?".
Best left to a gunsmith