I agree that paper was expensive. I don't see evidence that paper was the paramount, much less primary cost, of book making, assuming that explains the italics.

I agree that paper was expensive. I don't see evidence that paper was the paramount, much less primary cost, of book making, assuming that explains the italics. Though I haven't looked hard. I think you've mixed up two writing materials. "Parchment" refers to animal-based materials like vellum, not paper. Yes, people scraped the ink off parchment. But according to https://en.wikipedia.org/wiki/History_of_paper https://en.wikipedia.org/wiki/History_of_paper , deinking of paper wasn't invented until the 1700s. The same source says in the 1300s or so, the price of paper was about 1/6th the price of parchment, "and then falling further." Your cost model says only that the labor for removing ink from parchment was less than the price of making new parchment. For made up numbers, let's say the effective price to make new parchment was $15,000 and the price to scrape the ink off was $10,000. How does that help figure out if the price to copy was $4,000 or $40,0000?