The batteries are the single biggest cost in an electric car. The rest is all much cheaper than a conventional car. Replacing a your batteries would be a significant cost compared to buying a new car. It might even be 1/3 of the new ticket price.
Last I saw the battery expectation is around 15 years. In 15 years, at the rate of development of EV's and research/development being put into batteries, it would be reasonable to expect that batteries would be significantly cheaper with much better technology.