But it doesn’t have to be a structural exoskeleton. Nothing could be cheaper than stamping flat unpainted steel panels, and (I think) it would look better.
I started a thread on the Tesla forums called “Cybertruck discussion for engineers” that got a lot of interesting input on the pros and cons of using stainless steel as a structural exoskeleton. It has its advantages, but will be very difficult to get it right, and body damage will be very hard to repair. Nothing wrong with a tougher, badass “cladding” with easily replaceable panels though.