"Η εφημερίδα είναι φθηνότερη από το βιβλίο."

Translation: The newspaper is cheaper than the book.

[Anas276]

Are "Πιο φθηνό" and "Φθηνότερο" the same?

[spdl79]

They are indeed. If you want to form a relative superlative, you can do it either by using the article plus a πιο before the adjective, or the article plus a -τερός attached to the ending of the adjective.