The Logitech K400 Keyboard with built-in touchpad is on sale for $19.99. This matches the lowest price I’ve ever seen for this great keyboard. It’s touted by many, including myself, to be the best Fire TV keyboard in this price range. This keyboard uses a USB dongle to connect to the Fire TV, so it will not work with the Fire TV Stick.
If you want something a bit more sleek, the Anker Ultra Slim keyboard is just $9.99 after applying promo code ANK50OUT during checkout.