Painted piece of plastic gonna be cheaper than sheet of stainless steel. Stainless is significantly more expensive than typical materials used on car, which would be normal steel or plastic depending on panel.

Also painting IN THE FACTORY isn't expensive. Re-painting the part on repair is because of all of the prep work required (take apart, clean, color match etc).

Might be break-even, but I doubt it would be cheaper

"It will be cheaper" is a perspective of ignorant "smart guy" that thinks because he got successful in one thing that they can weight in on industry processes they have no idea about