alt Hacker NewsPainting cars is also a process that scales. If you want to do a great job on one car everything you need can be had for less than $3000 (inflatable spray booth, large air compressor, a paint gun, and lots of sand paper). A good job can be done for less (a cheap air compressor and paint outside can still get good results), and most people who want to paint a car already have most of the tools so the cost goes down. The above setup will also handle a small auto body shop that is painting a couple cars per month, and you can upgrade equipment as needed (I'd start with a spray building instead of an inflatable booth).
At the scale of Tesla the millions of dollars on a fully automated setup is cheap because amortize the cost of so many cars
Painting actually introduces some scaling issues in manufacturing. Any painting step prevents you from haphazardly mixing all the parts produced on a line. Most vehicles will have multiple lines that eventually converge across multiple suppliers. Painting forces you to either coordinate the production of each individual component so that they're all painted the correct color during final assembly (which becomes difficult if any parts fail QA), or buffer painted parts in a giant warehouse. There's other advantages to the warehouse, but I wouldn't call it cheap.
Very common to use a mix of both strategies in practice.