We will be staying in Positano for a few days in mid to late September and would like to see Paestum. Once there, we think we'll be fine with a self guided tour; but what is (are) the best transportation option(s)? Ed
Zoe is correct about your travel options. This tripadvisor thread will give you a lot of specific information: http://www.tripadvisor.com/ShowTopic-g187779-i161-k6104977-Positano_to_Paestum_day_trip_in_June-Amalfi_Coast_Campania.html
Car is the most convenient. You can use public transportation, but if you do I suggest spending the night in Paestum (it has the ruins, a very good museum, and a beach). You would need a bus/train or ferry/train combination from Positano, so you might be better off renting a car or hiring a driver, or ask your hotel if they know of a daytrip to Paestum.
For a scenic trip, take the boat from Positano to Salerno and catch the train to Paestum.
Don't miss the museum. I wish we could have stayed longer than the 45 minutes that we had for the visit. We were on a RS tour and we felt that they did not allow enough time to visit the museum while others thought it was too much time. I guess it depends on your touring style.
Don