Capot,
Typically Ryanair release their promotional fares about 3 months prior to the departure date. If you book quickly after a new month tranche is released there is generally good availability, especially in the off-peak months.
As someone else alluded to, Ryanair have been subsidising the APD on a number of fares for years. You need to carry hand baggage only and pay with a visa debt card but the cheap deals are readily available.
I should also add that its not just price I’m attracted to - I must have taken 60 sectors in the last few years, none being delayed for more than 30 minutes.
Smala01