Free for all, both ePub and Mobi formats. It currently runs $14.99 on Amazon, but according to the publisher, it will soon be free there as well (which makes it a lot easier to get onto a Kindle as the Mobi file is 150MB.
http://www.esv.org/e-books/
Also on the same page, you can get a free copy of the ESV Bible, but that's been available freely in multiple locations for a long time.