Newegg offers the refurbished Logitech K480 Bluetooth Keyboard in Black, model no. 920-006342, for $20.99. Redeem this $10 mail-in rebate to drop the price to $10.99. With free shipping, that's pennies under last month's per-unit price (you had to purchase two keyboards) and the lowest total price we've seen. (It's also the best price now for a refurb by $18.) It features 81 keys and a wireless range of up to 30 feet. Rebate expires December 31.
A 90-day warranty applies, although it's unclear who backs it.