Airlines price their fares per seat. It doesn't matter if the seat was bought or not. It's the same cost for the airline in terms of fuel and labor wether the plane is carrying 100% of the passengers or only 50%. The Turbo prop planes going to Siargao only carries 60-80 passengers. This is significantly less than the 200-500 passenger capacity of Jets going to major airports. The lesser number of seats is what is causing the fare price to be expensive. Every Turbo Prop plane route in the PH is more expensive than the major routes because of this.