I think what you're saying is unnecessarily pessimistic. Lots of things evolve quickly in a period of 5 years in technology. If Tesla claims it will develop a $30k consumer car, I'd say they probably know what they're talking about, and they'll probably build it with quality. I mean, what's the point of going this far, if Musk just wants to piss away all of his credibility by making a crappy $30k electric car? If you want to guesstimate costs and hack them together, we can do this all day, but I'd say the only way to tell is to wait and see.
TL;DR - it's hard to make claims to the quality the next Tesla car without having any idea of what they're going to do.
TL;DR - it's hard to make claims to the quality the next Tesla car without having any idea of what they're going to do.