To what extent was materialism driven by economic interests versus idealism during Germany in World War II?
I assume that you are talking about materialism here in the Marxist sense and are asking whether the conditions in Germany during the Nazi era truly were driven by economics rather than by ideology.
A Marxist would argue (as in the wsws.org link below) that the Holocaust arose out of capitalism and imperialism. The needs of German capitalists led to the desire for imperialism to gain lebensraum. The German capitalists thought the Nazis would be the best way to achieve this imperialism and so they let them have power, leading to the Holocaust.
But this does not ring true to me. Let us say, for the sake of argument, that economic factors (rather than Nazi ideology) led to the desire for more land. Economic interests, then, have explained some of what was going on in Nazi Germany. But why the Nazis in particular and why anti-Semitism? These things are not made necessary by economic conditions. It may be that economic conditions allowed them to happen, but they did not cause them. These things are rooted in ideology, not in economics.
Overall, then, I would argue that it was economic (and geopolitical) factors that led Germany to start WWII. However, it was ideology and not economics that led to the details of what Germany was like during that time.