Unfortunately, it is no longer possible to post your eBook for free on the Amazon.com Kindle store. Despite free shit being a great way for a writer to build their brand name, the minimum price you can set on Kindle is $0.99 with a 35% royalty. However, if you look at the legalese in the Amazon.com pricing page policy, you find this nugget.
From time to time your Digital Book may be made available through other sales channels as part of a free promotion. It is important that Digital Books made available through the Program have promotions that are on par with free promotions of the same book in another sales channel. Therefore, if your Digital Book is available through another sales channel for free, we may also make it available for free. If we match a free promotion of your Digital Book somewhere else, your royalty during that promotion will be zero.So in regards to your eBook being free, the all-powerful Amazon.com decides. The best way to trick the oracle is to make your eBook free on Smashwords and hope that Amazon notices. I've been trying this with a 1,100-word short story called Curfew, but to no avail. It was first free on Smashwords, and then I tried uploading it to Kindle with the minimum $0.99.
I'm going to attempt another method to trick the gurus at Amazon.com. I published the Bunker below Believers' Palace at Amazon and Smashwords for $0.99. Today, I've made the story free at Smashwords. Hopefully this will be a convincing enough deliberate action to convince Amazon.com to also make it free. We shall see.
Bunker below Believers' Palace for free here at Smashwords, and hopefully at Amazon.com soon.