Zondervan’s NIV Application Commentary series is on sale again (today is the last day), with each of the ebooks selling at $4.99.
I really liked Psalms vol. 1 in this series. There are a lot of really good volumes in NIVAC, including some e-bundles available now.
All the Table of Contents now are hyperlinked, so navigating via Kindle or iBooks should be relatively manageable. You won’t get the same sort of search power you’d get in Accordance or Logos, but the price is tough to beat.