> Printed books - > 300-400 € per semester. Ebooks from questionable sites - > free. + more and more material is from papers instead of books so pdf were easier unless you wanted to pay 20 cent per page printed at the university printers.

As a student (or even researcher), you often gets these papers from similarly "questionable" websites because the typical university subscription for academic journals is not as encompassing as you need it for your studies/work.