$0 cost
http://www.baenebooks.com/ http://oreilly.com/ http://www.smashwords.com/about http://www.ebooksjustpublished.com/ (seems to be a blog for above site) http://drmfree.calibre-ebook.com/ http://p2p.wrox.com/content/blogs/jminatel/all-wroxcom-wrox-e-books-drm-free... http://blog.text2go.com/2008/01/04/the-top-13-drm-free-ebook-sites/ google search "drm free ebook"
O'Reilly sells books from a number of publishers, all of which presumably support DRM-free formats. Some publishing companies such as SitePoint (where I happen to work, http://www.sitepoint.com/) and No Starch Press (http://www.nostarch.com/) also sell DRM-free formats direct from their respective websites. Various magazines also publish in free formats, such as Linux Journal (http://www.linuxjournal.com/) which I currently subscribe to. Atomic MPC mention on their website that you can buy a digital subscription from them in PDF format, but last I checked it wasn't actually a PDF and required proprietary (possibly DRM-encumbered) software just to view it - a plain case of false advertising. I actually wrote to Atomic about this, and the response was basically "We're new to this, give us a break, use a real computer if you can't read our format". Needless to say, I don't read Atomic any more. Regards, Adam