You ask why it is so expensive, before I say why it is expensive, would you prefer to be like Africa where Airlines cut corners and crash regularly? when you are at 40,000ft the outside temp is approx -40C, no oxygen and only a few lbs pressure, not the environment to be skimping on cost! its not a taxi, there are no laybys up there.

You are paying to stay safe, the spares cost a fortune up to $8,000,000 for an engine (which can require major overhaul if hit by a bird (approx $2,000,000)
The Pilots, Flight crew and Engineers all have to be trained and retrained every two years.
The industry is extremely well regulated with audits and checks by each nation on the other aircraft when they visit abroad.
All this has to be paid for.
We all know what happens when the driving force is money and not safety.