Not the OP, but that's an interesting question! Some googling got me to a quote of "Jehan de Sanlis made this for 6 pence per quire", The Hague, Royal Library,

Not the OP, but that's an interesting question! Some googling got me to a quote of "Jehan de Sanlis made this for 6 pence per quire", The Hague, Royal Library, MS 71 A 24, 13th century from https://brewminate.com/making-medieval-manuscripts/ https://brewminate.com/making-medieval-manuscripts/ ; I'd guess that illumination and binding these quires (16- or 24-page sheet) doubles the price, so we're at half-pence per page; price summaries from a slightly later time (but different place) like http://faculty.goucher.edu/eng240/medieval_prices.html http://faculty.goucher.edu/eng240/medieval_prices.html have similar values (~240 pence/ book) and indicate that a small house costs 500-1000 pence, so a house costs something like 1000-2000 pages worth of books, and it's worth taking into account that medieval manuscripts put less words on a page than modern paperbacks, so the same book would be more pages back then. From a different perspective, copying the Bible was said to require 15 months of work (Life in a Medieval City, Joseph and Frances Gies) and the price a small house seems to generally be in the range of 1-2 years salary, so a copy of the Bible - which is on the larger range of books - would be comparable to a house. In any case, an average codex at the time is less than the price of a house but on a similar scale, a collection of a hundred books is comparable to a fancy mansion in the capital.