After reading their SEC filing I would push back on that slightly.

I think the main reason Ryanair is so cheap is that they get insanely good deals with the airports because they bring so much business to the region. Ie Alicante, a secondary airport, is somewhat tourist-dependent.

Ryanair makes a deal with the municipally-owned airport and says hey, we're going to bring thousands of Brits and Germans to you (with full wallets). The municipality gives a good deal in return.

There's also the 1.5x revenue multiplier from ancillary revenue.

Finally, they only own one type of airplane. Makes the maintenance etc easier.