Before I go any further, some caveats about my analysis.
First, I built an accounting model, not a cash flow model. I wasn’t sure at that time whether I was going to purchase outright or finance, so I left that out. Later on, a friend, Travis, built out a cash flow model. The results are slightly different, which I’ll discuss below.
Second, I made a lot of assumptions. The model is very sensitive to the rate of depreciation. For the Model S, this is difficult. The car is fairly new, and resale values are insanely high. So we looked at Roadster values, thought about wear, tear, and battery replacement scenarios eight years down the line, and tried to get to a common sense number for how much a car would go for. How much would I pay for a 2006 model year car, today in 2014?
Third, I also left out some stuff. For instance, I left out insurance, because it’s too particular to driving history, and because I was lazy. I was also too lazy to try to translate safety ratings, HOV lane access, cargo space, and other features into a dollar figure.