I don't know about the humanities, but we did something like this at my old press (the National Academies Press, www.nap.edu, technically considered a university press). All the books are available online for free, in a form which I believe is searchable but which is not easily printable. While I was there we started offering all the books in PDF form at a slightly reduced price (free to scholars in developing countries)... it was a logistical nightmare, but it started taking off to some degree even during my tenure there.

Here's a 1999 article by the director on putting the texts online: http://www.press.umich.edu/jep/04-04/pope.html
and the results of the "PDF experiment," which was intended to plumb people's interest in PDF books:
http://aaupnet.org/resources/mellon/nap/