Don't believe for a second the school made ANY profit. If schools make more than about £50 profit on a trip they are legally abliged to refund the money. I have run overseas trips for years and to be honest £80 for that seems incredibly cheap. Trust me coaches, ferries etc for school trips are VERY expensive.
I have to agree that schools don't make a profit but you do have to question how Scouting and Guiding manage to put on very similar activities for MUCH lower prices.