If you want to do it the most affordable way....take the bus to central station (about 1E, which is a couple blocks from hotel. Then, take the Circumvesuviana for about 4E. You buy a ticket at a newstand outside the station. It's a slow but cheap way to go. Buy your ticket on the way back and it includes the bus back to the hotel. You can walk to the port for the ferry. We did not need a guide at Pompeii. You can download for free a Rick Steves Audio walking tour of Pompeii and it was great. Beware of 'flat-fee' taxi's from the train station to the hotel. If you are arriving by air, the "Alibus" is cheap and fast. 2 stops from the airport to a couple of blocks from the hotel.