The number of passengers on board does NOT affect the price of the flight: indeed costs refer to the rental service of the aircraft. It might affect the price of additional services calculated according to the number of people, such as catering.
The cost of the PASSENGER LUXURY TAX will be charged separately (Art.16 of Leg. Decree 06.11.2011, no. 201, converted, with amendments, of law 22 .12.2011,
no. 214 as amended: 10-bis “The tax due for each passenger and each way is 100 euros for flights up to 1500 km and 200 euros for flights longer than 1500 km. The tax shall be charged to the passenger and paid by the carrier.”).