I estimate the battery alone probably doubles the price, but you have to start somewhere.
I read an article a little while ago about a guy who had an older Nissan Leaf, and the battery was just starting to wear out. He bought an aftermarket battery online. In the few years he had the car, battery tech had improved quite a bit (as it is expected to do) and the direct fit replacement battery charged faster, held more range and provided more power.
This meant he had to download an aftermarket software fix so the car could accurately read the new battery, but he did the swap with a few wrenches and a pallet jack, at home, in his own garage. And, he was able to recoup most of the cost of the new battery by selling his old one.
All in all, he was able to give his car a serious upgrade in a few hours, and for a lot less than buying a new car.
That really appeals to me, as I am one of those jackasses that gets really attached to their cars. Being able to keep the old car that I am comfortable in while also being able to give it that "more peppy new car" feel every few years just by replacing the battery seems like a win/win situation.
Def