There is a Blue Book of Handguns that should give you a start. But the "value" depends a great deal on the condition the piece is in.
What is the serial number?
Is it in the original box?
There is an American Derringer website and you can probably float queries around e-bay and amazon-ville to get a clearer direction.
Good luck, doc
This would be a Davis Arms .22 Caliber Derringer.
5-100 USD depending on specifics
Fairly obscure 22 derringer, made in Germany by World Arms. Value in the $50 range.
$50-$75
10-100 usd
The value for a Savage Arms 284 caliber is actually dependent upon a number of factors. Some of these factors include the age and condition of the firearm.
Depending on condition, $50-$100
400-600. Very rare
5-35 usd
North American Arms
25-60 USD or so
Steve Petranto