You do have another choice, the sants train station is also where the underground is as well so you can explore the city without too much cost, also on returning to collect your luggage there is a train which takes you straight into the airport, cost i think is 6 euros each, the staff were very helpfull, they have an information booth for the underground at which they speak english, and we had no problem getting the train. Luggage storage is well signposted. Barcelona has some fantastic buildings, also if you want to shop placa cataluna is the main square with plenty of shops leading off. you can get the underground from sants to there, have a great cruise.

Cab is cheapest at around €30. There will be hundreds lined up at the airport when you land. When you get off the ship take a cab to Barcelona Sants train station where there are luggage storage facilities - approx €4.50 per locker. Enjoy the day in town and then catch cab back to airport at the end. Couldn't be easier.