What is the cheapest way to travel from Netherlands to Italy?
Where are you departing from in Netherlands and where are you arriving in Italy?
Walk and live off the land in transit.
No really, in general, flying and taking the train can both be pretty cheap depending. But flights from various Dutch cities to various Italian cities start around $30 on low cost airlines, no doubt some up charges for a bag etc. such a deal.
www.skyscanner.com to find cheap flights in Europe. Rotterdam to Bergamo, $109 on one date.
Best site for finding flights: https://www.kayak.com/flights