Purvey doesn`t collocate there. To purvey means to pass a gossip or something that should not be circulated.
The expression that best goes there is:
"The most significant advantage Internet can bring us is that it becomes a library that..."
The rest of the sentence is not okay. Perhaps due to the mistakes corresponding to punctuation. The fact is that I couldn`t get what you mean.
You should have said:
"The most significant advantage Internet can bring us is that it becomes an, if not the most, extensive, cheap and quick library that everybody can afford."
Student or Learner