It's not just the price, but also how "legitimate" the registrars are and how well they deal with abuse.

Here's an anecdote: I know someone who insisted on using a .tk domain for legitimate business purposes for many years. When I heard of this, I immediately asked "isn't that the TLD managed by a shady company that gives domains away for free and then steals them back if they become popular?" He insisted this did not affect him, as he was a legitimate customer who had been paying for the domain for over a decade.

Fast forward a few years, the company behind the TLD (Freenom/OpenTLD) went under due to their shady business practices, he lost the domain, and was told he had to register it again at a new registrar for a much higher price to recover it.