We booked our trip (27th of March) long before Christmas as a present for our daughter. The cost for the 3 of us, tickets, flights and accommodation was the same as the school trip they had planned (coach, ferry, one day in the park) which she really didn't want to go on.
Keeping that a secret until Christmas day was a nightmare, but so worth it. I'm sure that keeping it quiet will pay off in the end. Have a fab trip!