BlutekUSA via Amazon offers Prime members the factory-refurbished HP K4000 Wireless Bluetooth Keyboard for PC, model no. E5J21AA#ABA, for $10.99 with free shipping. (Non-members can spend $49 or more to qualify for free shipping; otherwise, shipping costs $8.64.) Outside of the mention below, that's the lowest total price we could find for a refurb by $4. (We saw a new one for $4 more in June.) It features Bluetooth connectivity, Android function keys, Windows Function keys, and it is compatible with Windows 7, 8, and 10. A 90-day HP warranty applies.

A close price: Altatac via Walmart has a refurb for $11.95 with free shipping.