SpaceX (another of Elon Musk's companies) has achieved similar feats in the realm of space flight.

According to his biography <https://www.amazon.com/Elon-Musk-SpaceX-Fantastic-Future/dp/..., Musk is particularly good at identifying supply-chain components that can be economically produced in-house. The Gigafactory looks like the same general strategy, and if it pays off as well as the SpaceX case has, they have a good chance of achieving their production goals.