The online store at
crossway.org is offering
all of their ebooks for $5.99 (or less if the price was originally lower) until January 15 and this includes all of the ESV study Bibles. There's also a Greek-ESV parallel New Testament. All ebooks bought from their site are DRM free and can be downloaded in both EPUB and mobi formats with the same purchase.
As far as I can tell, there's no quick button to browse ebooks, but search results can be filtered to include only ebooks. A search for "a" filtered for ebooks returns 513 hits. Here are links to the study Bibles:
ESV Study Bible
ESV Student Study Bible
ESV Global Study Bible
MacArthur Study Bible, ESV Edition
Greek-English Parallel New Testament