I suppose it depends on how much information (data on spreadsheets) is available about the books - and if the family has already created any finding aids for searching specific content in the collection. It also probably isn't just books, it may well include what is called "vertical files" or paper clippings, journals, albums, cassettes, CDs - and then there is all of the art that is sometimes in these collections.

The more the library has to work with the collection to integrate it into their system, and to dedicate someone (who may not already be on staff) to do the work - it isn't necessarily huge, but it isn't small, either. Endowments can be open-ended, we had one that worked for years to reach $400,000 to host a huge number of historic maps. They did regular fundraising over a course of several years to add to that goal.