You need to seek a professional appraisal.
Need a detailed description of all markings, barel length, caliber/gauge, sights, condition, accessories, etc.
What are the markings on the pistol?
You will need a professional appraisal
Need to know who made it and what shape it is in.
50-180 USD
It appears that this is a Colt New Model Pocket Pistol Of Navy Caliber. The engraving on the cylinder should say Stagecoach Holdup.
10-100 usd
50 USD or so
Which pistol? Most production pistols have a barrel length of 1 to 8 inches.
Low cost, probably French.
Try to cock it while pushing a cleaning rod down the barrell
217 mm