I don't know of any data that supports the contention that operating a digital library is less expensive than operating a traditional library.  While I agree that there are many advantages to digital libraries over print ones, the proposition that cost is one of them is pure opinion and not supported by either anecdotal or qualitative research from the likes of Outsell and others.  Costs that are lower (floor space, circulation infrastructure, etc.) or easily offset by costs that are higher (software, programming, hardware, etc.).    Roger