Back in the late 60's-early 70's , I use to charge $10.00 labor + price of strings(back then strings were cheaper and I did have a dealership with a major co. back then so string prices were low, as compared to now, as I started stringing again since last Dec. after a good long break).My prices now are string price + labor, as I know what my time is worth, but for friends, I only charge string price only. (seems like I have more friends now!)
You just have to figure what your time is worth, I know others here string very fast, I like not to be rushed, take my time, and check everything over carefully. When I get a racquet, I check the frames integrety for cracks, cut out the strings, check grommets, mount racquet, measure out string, and I have not even started stringing yet. All this time adds up, and should be figured into your price. Just 2 weeks ago, I got a racquet from someone that I hit with, I paid especial attention to this one as When I played against him before he threw his racquet, and then kicked it into the fence. Needless to say there was a small crack in the frame. Had I not seen it, I most likely would have broke when I would have started to string. I avoided the whole situation by checking it carefully, which should be done on all frames you recieve. If I broke that one, and only charge $10.00 / racquet I would need to string a good # more just to break even.
In other words keep a # of factors in mind as to your time and expenses, as to what to charge. When I last went to midas muffler, their labor charges were $98.00 / hour , and almost anyone can do minor auto work, but do you want anyone to string your racquet?
