We are planning a trip to Positano in Oct 2012. I have been racking my brains on how to make the trip from Naples to Positano using public transportation (shuttle is about 100 euro each way).

As noted, I am told that the ferry service from Sorrento to Positano is likely a no-go. So it's Naples to Sorrento to Positano by bus. Or another option someone suggested was Naples to Salerno to Positano by bus (there's also a ferry i understand from Salerno to Positano).