Cheapo airlines in Europe don’t all go to secondary airports, although they often do. However they often service secondary destinations. For example, we flew Basiqair to Bordeaux last year from Amsterdam. Not exactly Nice. To get to Milano, some of the low costs fly to Bergamo instead, which is on the Venice side of Milan. Their fares were a fraction of the majors — Air France and KLM. In addition to the airlines you mentioned last time, here are some more choices.
– Louis Rossetto
And a broader list from Germany.