10-27 Estimating a cost function, high-low method. FlyHigh Vacations offers helicopter service from suburban towns to Heathrow Airport in the United Kingdom. Each of its 10 helicopters makes between 1,000 and 2,000 round-trips per year. The records indicate that a helicopter that has made 1,000 round-trips in the year incurs an average operating cost of $350 per round-trip, and one that has made 2,000 round-trips in the year incurs an average operating cost of $300 per round-trip. 10-27 Estimating a cost function, high-low method. FlyHigh Vacations offers helicopter service from suburban towns to Heathrow Airport in the United Kingdom. Each of its 10 helicopters makes between 1,000 and 2,000 round-trips per year. The records indicate that a helicopter that has made 1,000 round-trips in the year incurs an average operating cost of $350 per round-trip, and one that has made 2,000 round-trips in the year incurs an average operating cost of $300 per round-trip