Musk claims that they should last between 500k and 800k km, and there is evidence to back up that they do last some time (although, with not much time under the belt, it's hard to say) which is more than the typical 300k (if you're lucky) on an ICE car. And the current price of replacing the battery looks like it's in the 13-20k range. So not way more than the car itself, although maybe you are talking used.