Update: This deal is still available even though Amazon Prime Day has ended.
Through 7/31, Amazon Prime members can get a 3-month KindleUnlimited Membership for only $0.99 (normally $29.97 – savings of 96%). You must be a new Kindle Unlimited member to get this deal. After the 3-months, you'll be charged $9.99 a month, if you don't cancel.
If you prefer a longer membership, you can save up 40% off a 12-month or 24-month Kindle Unlimited Membership (making it only $80.32 for the year or $143.86 for a 2-year plan) when you use coupon code PDKU18 at checkout.
What is KindleUnlimited?
Choose from over 1 million titles in the Kindle Unlimited program, and get unlimited reading and listening (on titles that state “Kindle Unlimited with Narration”) during your membership period. You can give KindleUnlimited membership as a gift. Amazon will email the recipient with redemption instructions on the day you choose. Recipients can immediately start their Kindle Unlimited membership or exchange it for an Amazon Gift Card.