Impossible to answer without knowing who made it.
AFAIK, Colt never made a single shot pistol
50 or so
Impossible to answer without the serial number.
50 USD
Check the frame, barrel, butt and under the grips
Impossible to answer without the serial number.
10-100 USD or so
60's or so
No serial number provide; 50-850 USD
Buy some books that deal with the type you have.
take out the screw @ the bottom of the handle take handle off serial # is on left side
'K' prefix to serial number indicates 1950.