For Prime members only, Amazon offers the Logitech K380 Multi-Device Bluetooth Keyboard in Blue, model no. 920-007559, for $21.99 with free shipping. (Best Buy via eBay offers it for the same price via pickup.) That's $8 under our May mention and the lowest total price we could find by $3. It features the ability to connect to three different devices and switch between them with a button press.
Update: Amazon is now offering this item through other sellers, but Best Buy via eBay still has it for $21.99 with in-store pickup.