In the 1970s the Caledonian Moonjet overnight fare was £13 return for Belfast to London. BEA's overnight Vanguard seats were even cheaper, I believe.
Air fares were regulated and much more expensive in those days. Who in their right mind wanted to fly at those times anyway? No public transport at either end as well. Yield management drives the profits that are invested in the new equipment which opens new routes which drives the profits etc. Regulated air fares made sure the market was stagnant.