The item listed is a NON-FIRING replica of the type of firearm used to assassinate President Lincoln. That make and model is listed on Amazon at $40.39.
I THINK your derringer may be a RECK. Value about $25-$50.
10-60 usd
50 or so
100 or so
50-260
50-260
20-40 or so
40-100 USD
$75
50-80
$75
10-100 usd