You can take a taxi from Marina Piccola to the center of the city. You will avoid a steep and challenging hike. Also if you want to go to the train station or SITA bus station for an excursion out of town, you will save a lot of time by taking a taxi. For a ride of 3 km and 5 minutes you will pay approximately € 10 per taxi (4 persons, one way).
TIP: Keep in mind that the taxis at the port of Sorrento are rather scarce.