When I leave Positano I will need to get to the Salerno train station. It doesn't look too far. Any ideas?
if you'll go to Salerno during the winter and spring time there are no boats; you'll have to use the SITA bus to Salerno. It takes circa 2 hours. You'll be better off if you use the train in Naples instead, much closer to Positano: you'll have to use a bus to META di Sorrento (20 minutes ride) plus 1 hour train to Naples.
This seems to be a more fun and much cheaper route than the typical Naples/Sorrento route but one not often travelled?