TechRabbit has the Logitech K480 Bluetooth Multi-Device Keyboard in black or white for $19.99 with Free Shipping for a limited time. To get the discount, use the coupon code: LOGITECH10 at checkout. Deal expires May 7, 2016.

Newegg through ebay has it in black for the same price with Free Shipping for a limited time.

The Bluetooth Multi-Device Keyboard K480 is a unique keyboard for your computer. That also works with your tablet and smartphone. The Easy-Switch dial lets you switch typing between 3 connected Bluetooth wireless devices, and you’ll find a familiar keyboard layout with shortcut keys for Windows, Mac or Chrome computers, as well as Android and iOS mobile devices.