The conclusion that an account being cheap is the problem as a reason for regulation is a disturbingly wrong-headed on multiple levels. It essentially says. "If only superpowers can use it would be a-okay!". A monopoly on manipulation is a bad thing for the same reasons allowing only incumbents to run political ads would be.

running political ads is in and of itself value neutral, tools for manipulation aren't. Just having them in the hands of fewer people is a straight up win in the same way having bioweapons in the hand of fewer people is. "I wish everyone had Sarin gas to level the playing field" isn't really a great idea.

I think a minimum pricing on accounts, even if it's just a buck or two on most social media sites would do very little to hinder genuine participation but probably eliminate or render transparent most political manipulation.

Arguably the primary reason nobody does it is because it would reveal how fake their stats are and how little value there actually is in it