The Belgian Grade III Semi Autos can run between $3500 to $7500 or more depending on the vintage/condition and the engraver. The earlier Belgian versions come with the older 'wheel sight' and have slightly heavier engraving.
The later versions seem to have slightly lighter engraving but are still very nice.
'Camster' on Rimfire Central/Browning section can tell you all about them, he's a great resource.
If you can, please post pictures of your grade III.... also the serial number should help you with the date. You should be able to spot the engravers signature...
The receiver should have a 'coin' finish and not nickel (I think).