The perfect price is the price the punter is prepared to pay. Cost of production is irrelevant.
I can imagine in some circumstances somebody might be prepared to pay $100 for a hotdog, or $50 for a gallon of gas, or $10 for a sandwich (see LCC's on-board pricing). Of course I'd be called a bar-steward for selling at 'unethical prices', but so what. In a capitalist world the law of supply and demand is paramount.
I also doubt that anyone in this industry could actually tell you what it costs to move a passenger, even a typical passenger, from point A to B. Too many variables. Fixed costs might be easy, but variable costs would be impossible to isolate down.