Some rough numbers to think about, in US dollars for a typical legacy --
Fuel Burn B777 CDG
would be about 115,000 pounds, plus or minus. At $2 per gallon enplaned, that's about $34,000 of fuel.
Maintenance for recent B777 might average $800 per block hour for an airline with global capabilities, plus overhead allocation for inspectors, parts warehousing, and the like. So figure $7,000 in total maintenance.
Navigation and overflight fees would be about $2,000. Landing fees at JFK
are roughly $3,000 for a heavyweight B777.
Stations fees would have to include a departing passenger fee at CDG
(figure $10 per passenger), an arriving passenger fee at JFK
(say $14), security costs of $1,000, cleaning and catering preparation (galley loading and such) of $2,000, and cabin amenities (blankets, pillows, IFE content and such) of $1,500 per flight. Add catering of roughly $25 per economy passenger, $75 per business passenger and $100 per first class passenger, including liquor and spoilage. So with 200 passengers (5/50/145) station and passenger costs would be about $18,000.
Monthly lease rates on a B777 might average $800,000 per month. Add $100,000 per month for insurance and spares and total aircraft cost is $900,000. The aircraft will run 28 rotations in a typical month (assuming 1 day each two weeks for maintenance) so allocated aircraft rent and insurance per flight is $16,000 per flight.
For crew cost, a US airline would staff CDG
with an augmented crew (probably two captain rank, one first officer rank). Captains make $250,000 per year (being the most senior) including basic benefits, first officers $125,000, and a cabin crew of ten averaging $50,000 per year with basic benefits (again, the most senior are flying the route). That's a total monthly cost of $93,750 per crew. Assume five crews plus a reserve are staffed to the route. That's $8000 per segment in crew costs. Note this is just the direct trip cost -- fully allocated trip costs can be much, much more depending on the company's labor agreements.
So the direct trip costs might start at $90,000 each way, not including overhead. That overhead is hard to judge -- it needs to include things like airport lounges at each station, maintenance and quality assurance overhead, and the like, not just promotion, sales and executives. But a large airline like Air France or American is spreading that overhead across thousands of flights.