Impossible to attempt to answer with no information on make/ model. A serial number is NOT unique to only one firearm in the world.
35-100 USD or so
25-50 dollars
3'000 $
10-100 USD or so
Need more details
Blue Book of Gun Values
No serial number provided.
We need the model and condition, not the serial number.
Not with just the serial number.
The maker of your Derringer is no longer in business. Sorry-
No way to answer without a maker and serial number.
Impossible to answer without the serial number.