The value depends on the age, whether it was Belgian or Japanese-made and other factors such as level of engraving, choke, barrel length, extra barrels, and so forth. You would need to know those things. Then I would consult a good catalogue on collectible guns to get an idea. In round numbers, from $800 to several thousand.
A Browning model BPS magnum hunter/stalker in 10ga.will bring 415 dollars in 95% original condition.
100-400 usd
Need a detailed description of finish, condition, box, papers, all features and markings.
around one thousand dollars in good condition
10-500 usd
A Browning A-500g shotgun in excellent condition is worth about 900 dollars.
About $550 for plain barrel, $850 for vent rib. This is for EXCELLENT condition, lesser condition less $$$.
1958,or 1968.
50-600 usd
50-5000 USD or more depending on specifics
50-450 usd
Depending on condition and exact configuration; a few hundred to multiple thousands of USD.