Depends what you're flying and the level of facilities you want.
I like Muenster-Osnnabrueck EDDG. It has all the facilities of an international airport (including a Cat III ILS at each end and permanent customs), but a fee of less than EUR 20 for < 2 tons (+ usual DFS ATC terminal charge). The main terminal is a bit of a trudge from the GAT, but there are restaurants a short taxi ride away in Ladbergen -- but I can't actually find the one I visited and liked a few years ago.