The planes are so expensive because they're specialized planes meant to be in the air nearly 24 hours a day - this justifies spending a huge amount of money on improving their fuel efficiency. A friend who works in large commercial aircraft once told me that the break-even point for money spent redesigning planes to be lighter was $1,000,000 in R&D spending per pound of weight saved. Older models which are typically used for intermittent cargo service can cost just $20m for a 747.
Based on this forum thread [1] the marginal cost per pound to fuel efficienciy is about "0.0155 gallons per pound per 1,000 statute miles". Over a 737's life it may fly about 50 million miles [2]. Combining facts one and two results in a fuel consumption per marginal pound of 775 gallons. Current jet fuel prices are about $3.40 per gal [3].
Wow, thanks for the effort put into answering a passing curiosity!
Of course any change to the aircraft has many other downstream implications (ability to source parts for repairs, lifetime of the part, maintenance requirements), but it's cool to think that for an "all else the same" replacement that the bar is still so high.
With the falling costs of advanced materials I do wonder if next gen aircraft will be substantially different.
The challenge is with design, certification, and manufacturing (forming and joining), not with affording the material. Plus, high strength steels can bear more stress than titanium, although they weigh more. This may be needed for certain space-constrained components.
A 1 lb saving saves $2,600 in fuel costs over the life of the craft.
However, an airline's break even point is a portion of that (perhaps $1,000) because the fuel costs are spread out over the life of the craft and there is an opportunity cost to spending money on the more efficient plane.
Of that $1,000, the aircraft maker will only capture a portion of the value - the airline expects to do better than break even. The airplane manufacturer may be able to charge $500 more for the aircraft.
They might hope to make 2,000 aircraft for something big like a 787 (although that number varies a lot depending on the model). That's 2,000 units times $500 = $1 million.
If you could take a top spec model, cut the weight by 400lbs without effecting the crafts capability, you could certainly sell it at a premium yeah, it would be some difference between the current price and the fuel cost savings shedding 400lbs casuses over the lifetime of the aircraft. Cerium estimated $2,600 per lb over the lifetime of the craft so yeah, that's a ~$1,040,000 in value there.
