We used Sorrento Silver Star car services in 2014. The name of the driver escapes me now, but they were very prompt replying to emails. Picked us up in Atrani where we were staying, took us to Ravello, around 'the back way' towards Naples (not along the coast) to Sorrento and Positano. Amalfi would have been included but Atrani is a short walk to Amalfi so we didn't need to explore there as we already had. (Oh, checked my travel diary - Lorenzo was our driver). We had him for 8 hours. It could have been a little longer - he offered to take us a little further along the coast at the end towards Minori/Maiori but it started raining heavily at the time and we were hot/tired from our day (thank God for car AC!).
The Mercedes mini van was clean and Lorenzo was a great driver. I am not one to spend so much money - it pained me a little...lol, but with my mom along, I didn't want to try and do buses - and you know what? My mom said it was one of her favourite days. In the end, it was nice to have someone to take us around...point out some highlights then drop us...tell us to come back in 90 min or so and be there waiting.
When we did Pompeii, we just hooked up with one of the tour outfits at the train station near the Pompeii entrance. I honestly can't rem the cost (also 2014) because hubby first got tickets for the tour that went to Vesuvius (he told someone Pompeii but they sold him tix for Vesu) then we had to switch them and Pompeii was cheaper - I can't rem how much $$ went back and forth. But the guide hit the highlights - about 3 hours...then you could explore the rest on your own.
