25-50
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It depends which Dickson model it is. "Dickson" was a brand name applied to a number of firearms made by other companies.
If this is a "Dickson Special Agent", then it was made by the Spanish company Echasa and is a re-named copy of their model FAST. Echasa also made this pistol under license from the French pistol maker MAB as the "Echasa MAB GZ." Echasa made these pistols from about 1962 until 1968, when changes in US firearms laws made importing them virtually impossible.
Value depends entirely on condition. In general, factory nickel finished pistols are worth more than the usual blued ones. In good working condition, with factory magazines, all versions of the Echasa FAST typically sell for $75-$150 in late 2010. (They were also sold as the EA Basque, Liberty Arms, Falcon, Madison, and other names, but all are the same. They came in .22LR, .25, .32 and .380 caliber, with .22LR and .32 being most common.)
About $130
Unknown.
How much is a old black powder only 45 cal long barrel pistol worth?
50-500
50-175
20-70
About $50-$60.
20-100 USD or so
25-50 USD
50 dollars tops.
10-100 USD or so
Impossible to answer without a detailed description.