According to MOL, there will only be one, maybe two, low-cost operators still in business in the long-term. This was a statement made a few years ago.
Southwest, WestJet, JetBlue, Spirit, AirTran, Allegiant, SunCountry, 1Time, Mango, Air Asia X, Transavia, Vueling, AirBerlin, Germanwings, Wizz Air, Jet 2, Flybe, Virgin Blue, JetStar all probably have a view on the accuracy of MOL's gems of wisdom. Admittedly a lot of other airlines have gone, but there are plenty more out there other than this list, operating or about to take the plunge.
but their cost base differs from the 'big 2' in that they operate ageing B737s.
...that's French for "they no longer have massive lease payments to make".