I mentioned this in another comment: something like EnergyGuide [0] would be great for this case, that way manufacturers like Tesla could more easily and consistently communicate how their vehicles have a lower cost of ownership.

[0]: https://en.wikipedia.org/wiki/EnergyGuide

I also want to say, if Tesla was doing this in some shady way, e.g. not offering an easy way to view the true purchase price, or making unfair comparisons, I would be totally against what they're doing.