Did you know that you can often find online PDF versions of books for free?
I recently found a great blogpost at OpenCulture.org pointing out that lots of places with large catalogs (especially museums) are scanning their collections and making them available for reading online. For instance, check out MetPublications, the Metropolitan Museum's site offering “five decades of Met Museum publications on art history available to read, download, and/or search for free.”
In particular, for SearchResearchers, note this:
Clicking on the "Read online" link will take you to the full-view version of the book at Google Books. (For example, here's that book, "Adorning the World: Art of the Marquesas Islands" as seen on Google Books.)
These same folks previously offered 397 complete books free, including American Impressionism and Realism: The Painting of Modern Life, 1885–1915; Leonardo da Vinci: Anatomical Drawings from the Royal Library; and Wisdom Embodied: Chinese Buddhist and Daoist Sculpture in The Metropolitan Museum of Art.
Since then they've grown the online collection to no fewer than 448 art catalogs and other books besides. Those are all available for free, along with the 400,000 free art images the museum put online last year.
It's worth keeping your eyes open, just to keep track of what's available online.
Other Links to Free Content from OpenCulture.org:
800 Free eBooks for iPad, Kindle & Other Devices (Epic of Gilgamesh; Beowulf...) 
