Powell's really is a wonderful place. Anyone visiting Portland really ought to make a trip by there. You can pick up used copies of CS Lewis and even Carlyle there for a pittance. Recently walking through there I was struck by a display in one of the central aisles with a CS Lewis work that I'd vaguely heard of, but never read. It turns out it was a real jewel also: The Discarded Image.
The Discarded Image is essentially a guide to the Medieval world view. It's technically literary criticism I suppose, but you shouldn't hold that against it. Remember that recommendation I passed on to you back in this post from CS Lewis, to read old books so that you could get a better understanding of the common presumptions of our own age?
Well, besides the Victorian era, the Medieval era is a very likely place that you might turn. There are lots of wondrous works from that period, from such masters as Dante, Chaucer, Shakespeare, Boethius, and the like. Many of these works are exceptionally formative to our culture today--forming big pieces and whole tropes in a lot of our present-day mythic narratives. Just from the standpoint of being able to construct good reactionary propaganda, they're worth the price of admission.
CS Lewis marks that price of admission way, way down in The Discarded Image. In it he breaks down how Medieval European man thought, especially insofar as authors and poets wrote. You can get some of this from Carlyle, regarding his own era compared to the Medieval, in his Past and Present. He'll also show you how to channel a late Old Testament Prophet like Jeremiah, for no extra charge.
This is, I believe, CS Lewis' last published work, and it's from his day job, unlike his apologetics and fiction. But those of you who are fans of Lewis will find that once again, you're encountering an old friend.
Project Gutenberg, particularly Gutenberg in Australia, will mark the price of many of these old works down yet further for you. The availability of many of these works has never been greater.