Airline pricing is not, and has never been, based on costs. (Well perhaps pre-deregulation domestic in the US, but not really even then.)
The airlines price to get the maximum revenue per passenger km. So fuel costs come down and (some) reduce or remove fuel surcharges, fares go up - total price about the same. They are constantly tweaking their models to give them the perfect price - the one that you are willing to pay.
Want a cheaper price? Take connecting flights. That's about the only magic out there.
Well, try and avoid any airline you are a FF member of. They know they can charge you more than a non-member, and they do.
But remember, in one of their most profitable years ever (2014) the average profit per passenger was just over $8.