Mostly Low cost airlines industries have rich source of oil reserve or they make contracts with oil companies for years so that they can get more make their cost of operation minimum to increase their revenues.

 Most low cost airlines generally have ties with other companies. With these ties, they are able to get better deals compared to other airlines.

Other things also fall into factor such as staff prices, food prices, etc, etc. It all depends on their budget and what they spend it on.

Tom from FINDairlinecards