Even the 707 didn't really make it cheap yet. At least over here, the last significant price drop was after 2000 or so with Ryanair etc. with 737:s and A320:s.

Even the 707 didn't really make it cheap yet. At least over here, the last significant price drop was after 2000 or so with Ryanair etc. with 737:s and A320:s. Probably a new business model in other ways as well. Single aisle, two reliable high bypass engines. There were still DC-9 derivatives flying around but no more really. I bet you could calculate maintenance man hour per kilowatt hour for all sorts of engines. Even the old manual flight control operations without computers meant the amount of work hours per flight was big - meaning for an ordinary worker it would not be possible.