Who makes modern affordable blank (paper) notebooks / journals?

Moleskine is one option, basic art supply shops for drawing books by Canson or Strathmore. Consider making your own. Here are some links
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Barnes and Noble usually have several racks of diaries and notebooks in the front of the store.

And most good paper shops (which are hard to come by nowadays) will have a selection nowadays.

I have seen such things in stores like Big Lots, if you’re in or near New England try Christmas Tree Shops or Ocean State Job Lot. They are often much less expensive than you find in a regular retail store.

I would look in any dollar store for discount paper products. Also, sales area of office supply stores and stationers.

I agree with @marinelife. I’ve seen some nice ones in the office aisle of Walgreen’s, too.