Musk hopes to assemble the Model S at a rate of 20,000 per year. A Sport model is planned for after launch. Musk expects a $7500 federal tax credit on electric vehicles of a certain size will defray the price to $49,900. That is, again, if everything goes to plan. So far, little about Musk’s various post-PayPal enterprises, including a solar-panel installation business and a rocket factory, has followed an easy path.