Rome - Pompeii - Sorrento- Rome

Prices you're seeing on Italian Rail for Rome-Naples are consistent with what I paid for 2nd class in September. IC train I took cost just under 20 euro. ES train would have been about 27 euro and Arista train would have been over 35 euro. You could save 20% if Amica fares are available, but that's the best you'll do buying them in Italy. Circumvesuviana from Naples to Sorrento cost 3.30 euro in September, but cost could be just slightly higher with a stop in Pompeii. Circumvesuviana tickets can only be purchasd there - no discounts. Note that there's a train from Pompeii to Sorrento every half hour, so it would be easy to adjust your schedule if you decided while at Pompeii to linger a bit longer.

I was in Naples just about 2 weeks ago. The ticket is 10 Euros one way, for Regionale. IC or Eurostart is much more expensive and it's not worth it because the travel time is the same.
Try Trenitalia.com for timetable and prices.
Try to look at prices not longer than 2-3 days in advance. Otherwise the web site won'r display prices.

Laura,

Is there any way to stay in Sorrento for the night? We did a day trip to Pompeii, Sorrento, and Positano from Gricignano (south of Naples) and it was too short. We started out at 8am and returned home for the night around 9:30pm and did not have as far to travel. We still felt we did not have enough time. Also the Naples Archaeological Museum was great and really enhanced the Pompeii experience. If you can make it work as an overnight, you could go the museum on the way back to Rome via Naples. Please let me know if you need recommendations on lodging.
Have a great trip!

Sorrento is truly lovely to stay in, if there's any way you can swing that.

Another alternative that will buy you more time is to visit Herculaneum instead of Pompeii. This is especially true since you are planning to give Pompeii only two hours, when it really demands much more than that. Herculaneum, on the other hand, is the perfect size for two hours. It's also quicker to get to than Pompeii, being between Naples and Sorrento. The museum is Naples really is worth visiting and since they have a HUUUUUGE scale model of Pompeii, it's almost like visiting the site itself.

By the time you get to the gate at Pompeii you will be lucky to see it for 1 hour befor you need to go and catch the train to Sorrento. Id plan on 3-4hrs Pompeii and 3-4 in Sorrento. We spent 5 days in Sorrento checking out all the small costal towns and did a day trip to Pompeii (we had a car). Have Fun!

We were there 2 weeks ago. We bought the train tickets and seat reservations from Rome to Naples from a little travel agent located off the Campo dei Fiori. The ticket from Naples to Sorrento was 3.30 Euro. They also sold tickets that were good for round trip, and I believe there was a day pass. Just ask when you buy tickets. When you arrive in Naples, head to the left instead of going into the main hall and you'll see the little blue Circumvesuviana sign. The Pompeii entrance is about a 5 minute walk from the train stop. Have some Limoncello in Sorrento for me...