No, if it was designed to be a single shot, it's a single shot. It needs to be reloaded after each shot.
AFAIK, Colt never made a single shot pistol
http://www.gunsamerica.com/guns/976640103.htm
100-350 USD or so
Best left to a gunsmith
200
100 or so
100-300 USD
100-200 dollars.
How much would a 22LR single shot pistol ?
10-150 USD or so
H&R and I believe Rossi have single shot rifles with interchangible barrels.