On your 31' Bombay Clipper reef points presumably would be appropriate and even necessary. It sounds like you would be paying for 2-3 hours of labor and that's about right for a job but you certainly COULD put in the reef points yourself. Once you figure out how much sail area you want to reduce and where to put them (part of the labor time) you arguably don't even have to sew. Use a flexible urethane adhesive to glue reinforcing patches on both side of the sail, then set a heavy grommet through the patched area after it has dried. Add your reefing ties and you are done.
Why the used sails have no reefing points to begin with, and what that says about cheap used sails, is a whole other issue.