On the other side of that coin, when airlines were heavily regulated, most people couldn't afford to fly at all.

The "regulation vs. no regulation" stance is the wrong way to look at it. Airlines are still regulated, of course. Maybe some of the regulations we do have are unnecessary, some of the regulations we got rid of we should really bring back, and perhaps there are others that we never had that we need.

We can't be sure whether cost came down because of removing regulation or improvements in technology. We can only guess.