One of the best recent sources on the cost of producing medieval manuscripts is Rosamund McKitterick's The Carolingians and the Written Word, a book about ninth-century continental monasteries and their books.
In 135-55 McKitterick discusses several aspects of bookmaking and their costs. Purple dye, for example, which was used to dye parchment, was extremely costly. The price edict of the Roman emperor Diocletian stipulated that a pound of silk cost 12,000 denarii and 150,000 denarii if it were dyed purple. The cost of parchment dyed purple was increased by the use of gold for illustrations and ornamental letters. These lavish expenditures were the prerogative of royal ownership, McKitterick points out, and they were rationalized because the books so decorated were usually Bibles. The regal appearance of the book reflected the status of both its subject and of the owner, she writes:L "The written word thus becomes a symbol of royal authority and responsibility" (144).
Some of McKitterick's sources won't be available to you in the library, but you should read her section on the cost of books and look for studies that talk about the cost of books in Anglo-Saxon culture contemporary with the Carolingians she writes about.
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