Not including all the software in a given car is not likely to make it much cheaper as long as there's some car that needs it, since software is free to replicate. Of course there more to it than that; you might be able to get away with simpler computer hardware if you had fewer features. But if you need custom hardware anyway (like Tesla) then it's probably cheaper to just put that in every car.
Of course there's the self-driving stuff which is super advanced, but this is happening for high end cars anyway. I'm sure there are cheaper electric cars out there that don't have any fancy self-driving stuff, but they're probably still packed full of motor/battery software.