Is the cost for a water taxi ride from the airport to San Marco of 110EU for one person or the total price for your group of 4?
Its negotiable and you should be able to get all 4 of you for that price. If you have a lot of luggage they may want more. I paid 100€ for 2 with luggage.
The private water taxis are a set price for the trip, and will take up to 6 people and luggage ( we had 5 and Rhee was no extra charge for luggage).
The shared water taxis are quoted per person.
Ironic, I was just looking at this water taxi service this morning. Check out the link: http://www.venicelink.com/en/private-transfer-venice-0. You can get prices for your group and make reservations from website. This is much cheaper than Viator or Expedia. Good Luck!
If you use that link and set it for a transfer between the airport and central Venice the price jumps by €50----to €109. Same as the walk-up price quoted above, no deal.
To the OP's question.
You are booking the taxi for a private ride so the number of passengers assuming all people and bags fit doesn't affect the price.
1, 2 or 4 in your party, the ride will cost the same. it is not a per person fare.
It is a nice experience, much nicer than your typically taxi ride to/from the airport in other cities for sure.
Depending on where your hotel is, you might ride down the Grand Canal which is a nice treat.
We took the shared water taxi that we booked through VeniceLink. We paid 25 euro each one way and bought our tickets on-line before our trip. When you buy your tickets they will ask what time your flight is scheduled to arrive. We also pre-booked for our trip to the train station when we left Venice.
We went from the airport to San Marco. We were the last to be dropped off, so for our first time to Venice we got a tour of the Grand Canal and many small side canals as the driver dropped off the other eight passengers.