Circling back to the OP's question, in addition to some of the other sources that were listed in the thread, this is definitely a source worth checking for everybody. Even if you live in a rural area, a lot of folks can get access to county or state library systems that will allow rural residents to setup an account and loan ebooks online. I've been pleasantly surprised the last 5 years or so at the growing number and quality of ebooks available for loan in my local public library system (Seattle Public Library).