Just for comparison, not to say that it was better or worse, we had the concierge at the (large) Hotel Ambasciatori book a Mercedes sedan and driver from their outside limo vendor, Eurotravel [80067 Sorrento, Via degli Aranci, 9]. Enzo, an older gentleman with a heavy accent but good English took us to Positano, Amalfi, Ravello, and a brief stop to see the view in a fourth town. This was 8 hours, to/from our hotel, in May, 2014, for 255 Euros plus tip. We thought it was well worth it.
It is fair to point out that this was not a slick, rehearsed, professional tour guide. And, we had to decline a visit to the pottery factory - but once he understood our wishes, there was no pressure. I know from cruise excursions that over 50% of his clients want the pottery showroom. Indeed, we stopped to use the toilets outside the pottery showroom anyway! He handled all the parking, and was always where he said he would be, at the appointed time. I don't care if he went to school (?) with the guy who sells fresh lemon ices for 2 Euros! They were good ices.
You should also know that when we tried to book him personally for the transfer to the Naples train station, he said that "the office will assign the driver." In other words, he was an absolutely scrupulous employee, who refused to make a side deal - which I mean as a compliment, even if it's not what we wanted. You should plan a walking lunch in order to make the best use of your limited touring time. We got pre-made sandwiches on the square in Ravello, and ate while walking to the Villa Cimbrone gardens.
We actually had him drop us off in central Sorrento, planning to have dinner and walk back to the hotel. He recommended (no, I'd rather say "offered", or "mentioned") a very modest place run by his friends, Ristorante Angelina Lauro, which was just fine. It was not tourist-free, but there were lots of local families there too.