Howdy
I have three Single Sixes. These are the old Three Screw models similar to the one posted by Bannockburn. With this model, you must be careful and never load the cylinder with six rounds. Just like an old Colt, if you drop it on the hammer with a live round under the chamber, there is a good chance it will discharge, and the bullet will go where ever the barrel is pointing at that moment. Always keep an empty chamber under the hammer. The two on the left have the old drift adjustable rear sight, the one on the right has a rear sight adjustable for windage and elevation.
A single SIx made in 1974 will most likely be the newer, New Model Single Six with a transfer bar in it. If so, there will be two pins in the frame, rather than three screws as can be seen here. A transfer bar equipped Ruger is completely safe to carry fully loaded. If it falls on the hammer, it will not discharge.
Anything around $350 or $400 is a good buy for a used Single Six in good condition.
I got the 22 Mag cylinder with a couple of these. Personally I am not interested in shooting 22 Mags. Much too expensive and much too much noise. Ir I want more power I will grab a 38, or a 45, or a 357, or a 44Mag.