As one of its daily deals, THAT Daily Deal offers the Belkin Universal Bluetooth Wireless Keyboard for Smartphones and Tablets, model no. F5L137TTBLK, for $17.99 with free shipping. That's the lowest total price we could find by a buck. It features function-specific keys, iPad shortcut keys, and USB. Deal ends today.
Of note, this keyboard may be incompatible with Android 4.3 due to OS snafus.