I don't know how long this is going to last, but The Complete Sherlock Holmes
is currently free on Amazon Kindle. Click the link to get to the correct page.
Also, there are a number of other complete works for less than two dollars. For example, The Complete Short Stories of Edgar Allen Poe is currently .99 and The Complete Mystery Novels of Agatha Christie are $1.99.
I picked up the Sherlock Holmes book and am looking forward to reading the stories once again!