I was actually surprised when I discovered Amazon giveaways work rather well. You have to “buy” as many copies as you want to give away, but the good news is that it actually counts toward your ranking! If you lower the price before doing it, you can do so for relatively little cost. Some places charge your horrible fees to give away your book, which is ridiculous for us indie authors! Plus, they usually insist on print copies while Amazon lets you do a giveaway with your e-books.
This is one way to get Amazon to help promote your book. They do the distribution, which simplifies the process. I have found it to be one of the most cost-effective promotions available, especially if you lower your book price before setting it up.