I'd have to dig it up, but it's the warranty that makes the difference.
It seems that he was partly inspired to write this by "the TTAC reader whose response to Bark’s article on subprime buyers was to straight-facedly suggest that a working father swap his own minivan transmission in his apartment parking lot."
I used to own beater cars when I was in college and shortly after. I never paid more than $3k for one, and I did all of my own work, including replacing all of the brakes on one of the cars myself. But I like working on things, I already owned the tools, and I had access to good public transit when my car broke down. I would not recommend beater cars to most normal people.