The manufacturing cost of EVs will likely decrease if they are mass-produced, although maybe not that drastically - the cost of producing conventional cars has indeed decreased, but not by that much, in decades.
The sale price is yet another matter. Currently, EVs benefit from government financial incentives in a lot of countries. Remove those incentives and you'll look at the prices a bit differently, even if the manufacturing cost decreases.
And there's still the issue of the batteries, currently being 30% percent of the overall cost or over, and having only a few years lifespan. Not sure their cost will really plummet, unless of course we find a technological breakthrough. So they are a problem for the intrinsic value of the car and tie you to the manufacturer, at least until batteries become standard, which is going to be pretty hard to achieve for years to come, since currently batteries are a significant factor of competition between the manufacturers of EVs.