These days, every element of flying feels like a financial calculation. Is shelling out $80 for an extra six inches of legroom in premium economy good value? Is it worth paying $50 to check a bag into the hold? How about $12 for a mediocre sandwich? Or $4 for a bottle of water? Many frugal travellers would answer “no” to all of the above. But there is one perk that might be worth paying a considerable sum for: wiping out jet lag.