How much does First Class really cost the airline?

Probably 1.5 times flexY.

The rest is pure profit.

Even if it cost QF Aud$4500 for the expenses to do with a flight SYD - LAX, they will charge the pax as mentioned Aud$8500 to Aud$10000 one way.

They know they can get away with it.

Markup and pure profit.

They also put a price on the demand of sitting in F.  Closer to date of travel, airlines will only price up fares.

Cheapest F is EK's MEL/SYD/BNE to AKL/CHC.

Fuel costs of the flight times floor taken up by a first-class seat divided by floor area of the aircraft. Everything else is chickenfeed.

Most interesting discussion and after reading Chris's list again it got me thinking there is more to this than meets the eye.

The curse of making money must be the high percentage of upgrade and reward travel in First class. I expect airlines don't make quite as much from this end of the plane than we think. Some carriers like Air NZ have dropped First completely. Others we have heard are also considering their options here and some are picking their routes. Don't get me wrong when airlines have lots of actual real live fare paying PAX in First it's their highest yielding seats by a country mile but there is also a lot of risk for them here too.