1998 Ford F-150 starter and/or starter switch

I recently replaced my battery because truck wouldn't start. Everything fine for about 2-3 weeks. Then truck wouldn't start again. It tried to start but there was dead silence just as happened the first time. Interior lights work, dash lights and all gauges work properly. Took battery and had it tested and battery is holding a full charge. Guy at garage said it sounded as if it is the starter switch is not making contact. As I think back, there were a few times when I went to start the truck and nothing would happen. I thought maybe I didn't hold the ignition switch for that split second longer. So I would try again and the truck would start. It didn't do it all the time, but every now and then. Since I am too far away from my mechanic, what kind of labor is involved in replacing the starter switch and what can I expect insofar as approx. Cost.