2nd Hand Market
Most of the current electric fleet is fairly new, and as time goes on we'll see more of them coming up for sale as used vehicles. I don't think I'll be buying one though.
Most cars run just fine for 10 years or more with relatively little maintenance costs other than yearly servicing. Sure, you may get unlucky and buy something that needs a major repair e.g. new engine soon afterwards, but this is rare. In any case, for an older car you can often save money by using reconditioned parts from a similar car that has been scrapped.
Electric car batteries are probably not going to last for 10 years, certainly not if they're heavily used. A £10K battery replacement cost may not seem totally unreasonable on a brand new vehicle retailing at £30-50K, but it looks like a very expensive liability on a second hand one that's selling for £10-15K. And it probably wont' be sensible to find a cheap reconditioned part instead, as the batteries from scrapped vehicles may well be near the end of their working lifetime too.
Really these batteries should be considered consumables, and the cost of the eventual replacement factored into the running costs listed in the advertising. However, as things stand, the (rich) first owner of the car probably won't need to worry about that cost as the problem just gets handed down to the (poorer) second and third owners, so the claimed running costs just cover the bare cost of the electricity.
It'll be interesting to see what this does to the resale value of these vehicles when the second hand market for them reaches commodity status rather than the novelty it is now. I fear that Elon Musk has actually just invented the disposable car.
I note that some other manufacturers effectively lease the battery with the car, meaning they can be replaced without financial worry as long as you've paid the subscription costs. At least that way the running costs are kept honest.