I have highlighted the great work the Rob Bradshaw before but he continues to provide good, out of copyright, biblical studies as free PDFs. He most recently highlighted his digitizing of William Oesterley’s Commentary on the Psalms. You can check it out here.
By the way, although it is fashionable to dismiss older works as simply out of date, there is still nuggets to glean. Recently one of my students pointed out an interesting insight into a passage that I was not aware of. I thought perhaps that he had made a novel discovery only to learn that though the more recent commentaries had not noted the point in question, an older work had. Take up and read!