When you book Air2Sea, one way is one thing, round trip you have to use the same airline. Fly into Venice and out of BCN works fine, but you have to use the same airline. Research all airlines first.
prices , times, etc. Have your ducks in a row. Example we booked A2S from Tampa to Quebec one way. I wanted Air Canada, when I called and asked, they said United, they have a certain order in airlines to offer first. I asked for Air Canada, the said ok, and gave me 2 choices, one of which was mine. Business was 1800 and we got it for 595 with A2S, 2 people was less than 1800. Our flight home I booked myself, out of NJ, price was ok. Once booked you have to keep checking on your flights, things can change without notification. I have always found A2S cheaper and they have to get you to the ship. Start checking early, no telling when they open for your cruise, it is not real easy but worth the effort. If you are he first to book price is lowest, depending on # of seats at that price, then they start going up. Too long an answer, sorry