Update (2/3 9:45am): Inateck via Amazon offers its Aluminum Bluetooth Keyboard for $15.99 Prime shipped (Reg. $24) after promo code G6NEE6JC is applied during checkout. Rated 4.2/5 stars.
Hisgadget Inc (100% positive in the last 12 months w/ 37,379 ratings) via Amazon has the iClever Universal 7-Color Backlit Wireless Bluetooth 3.0 Keyboard for $19.99, but code LIWBC8VI will drop your total to $14.99 at checkout. It ships free for Prime members or in orders over $35.
It is compatible with iOS, Android, Windows and other Bluetooth-enabled devices. This model features 7 backlight color options, built-in rechargeable lithium battery that provides up to 200 hours without the backlight, an auto-power saving mode, and more. Rated 4.3/5 stars from nearly 60 Amazon customers.
Cross-Platform Compatible Works equally well with iOS, Android and Windows, with shortcut keys optimized for all 3 systems.
Comfortable and quiet typing The whisper-quiet, low-profile keys bring a whole new level of comfort to your fingertips. What’s more, keep all your most-used functions and media controls closer than ever Windows-dedicated hot keys.
Compact and lightweight At 7.5 ounces and less than a quarter of an inch thick, this Ultra-Slim Wireless Keyboard requires little space in your bag, allowing for more usage on-the-go.
System Requirements 1) iPad – All versions 2) iPhone – All versions 3) Bluetooth-enabled PCs or Laptops with Windows XP / Vista / 7 / 8 4) Bluetooth-enabled iMac / Macbook with Mac OS X 10.2.8 or above 5) Smartphones or tablets (not including Dell tablets) with Android 3.0 and above (with Bluetooth HID profile) 6) Windows Mobile 5.0 and above 7) This keyboard may not be compatible with the Mac mini.
Note: After 15 minutes of inactivity the keyboard will automatically go into power savings mode. Simply press any key and wait 3 seconds to wake it up.