Should the "600 ducats" part of the Rudolf story be dismissed for good?

[stegu]

* The most likely candidate acquisition he found was one for 600 florins, which would have been if I understand correctly about 333 ducats. This purchase was for a barrel of rare books:

Yes, but I believe that the information that was transmitted orally was 600 gold coins, which a misunderstanding of florin and ducats a couple of generations later.

Note on Guzy's translation: "a couple of" in English has the connotation of a small amount. I am not sure if this is present in the German "allerlai", which to me feels more like "all manner of", implying a large variety. 

German is my mother tongue and I am quite familiar with the early modern German, as I edited a book on a 16th century's manuscript. 'Allerlei" (in difference to "alle" (all) as written today means just a small variety of things, with a focus on the uncertainty of the number. My estimate for the "small barrel" would be roughly 10 codices.

Either the details from the Marci letter are correct, and the emperor really spent three times the Imperial library's annual acquisition budget on a single manuscript. In this case, records of this highly unusual purchase have not yet been found.

The acquisition budget of the library was pretty small compared to other art acquisitions Rudolf made, e.g. gemstones, for which he easily paid up tenthousands of florins. 

As the number of pages of the study was strictly limited I couldn't add my appendix of all book acquisitions I've found, but yes, 600 fl. would be just too much for a single manuscript. But for a small lot of precious books it seems reasonable.