See what they are selling for at Gunsamerica. http://www.gunsamerica.com/ That should give you a pretty good idea.
Go to Browning's website under Support then go to Date your firearm. Value of any used firearm depends upon condition and area of sale.
100-1000 USD or so
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?".
50-500 usd
100-400 USD
You have a 20 gauge 3" Hunting model manufactured in 1979. Depending upon condition $600-$1,200.
What is the value of a 12 gauge Browning shotgun serial J68824?
1972, on line auctions.
50- 10000 USD depending on specifics.
100-1000 or more depending on specifics
Manufactured by Remington for Browning during the 1940's while the FN plant in Belgium was otherwise 'occupied.' Valueup to $400.