What would be the cheapest route to travel from New York or New Jersey to Poland via air and train?
Check flights from JFK and EWR to Berlin (since 1945 only around 40 mins from the Polish border). CO and DL serve that route nonstop.
Have you checked LOT Air, the Polish airlines, or other eastern European airlines, such as Aerosvit(Ukrainian), Aeroflot(Russian), Finnair(Finland)....? Sometimes the national airlines of the country would offer the cheapest fare.