Our ebook store is based on Overdrive. At Overdrive, you can download free samples of WMA and MP3 files, but I don't believe there's free samples of ebooks available. I'll check.
http://www.overdrive.com/resources/drc/#test
You can do an advanced search on PDF titles with a price ="<$5.00", then sort the results by clicking on "price". There's several pages of PDF titles that are less than $1.00 each.
We're adding more titles as they become available.
Thanks, Troy