I would propose three highly representative films of three different karst rivers in our culture:

1) for the "low budget" series: "La croce dalle sette pietre", also known as "Il lupo mannaro contro la camorra": La croce dalle sette pietre - Wikipedia

2) for the "years of lead" series: "Milano odia: la polizia non può sparare": Milano odia: la polizia non può sparare - Wikipedia

3) for the "Franco & Ciccio" series: since my favorite has already been mentioned by @[Caspasian], allow me to pay tribute to the late E. Morricone with "Per un pugno nell'occhio": Per un pugno nnell'occhio - Wikipedia