>Can modern human life be sustained in a world where internet services become much more expensive?

Probably yes. The world of 1990 was not much less modern than the world of today. So it would all come down to the question of, how disruptive the de-Internetification of the world would be. A pre-Internet world is recognizably modern in most ways. But since we have come to rely on the Internet, the process of losing it could be very damaging.