Logos has a great free book of the month. Bervard Childs’ Isaiah commentary in the Old Testament Library is completely free…and you can add Leslie Allen’s Jeremiah commentary in the same series for only .99.
Just go to Logos, click on the Free Book of the Month banner, and get yours.
(Edit: the product page won’t be live until tomorrow. The link above will put both volumes in your cart. If you want more details about each commentary, here are the links to their individual product pages: Isaiah and Jeremiah.)