The ZTE Spro 2 was initially announced two years ago, and later available for sale through AT&T for $500 without a contract ($400 with an agreement). It's definitely an odd device - it's running Android with access to the Google Play Store, so you can project your favorite media apps without a connected device. Now you can get it for $399, $100 off the starting price.
Now you're probably wondering, "Why has it only dropped $100 over two years?" Well, projectors are generally expensive, and the Spro 2 has a decent 200 lumens of brightness. The resolution is only 1280x720, but ZTE says it can project up to a 120-inch image.
As mentioned above, it's running Android 4.4.4 KitKat (as far as I can tell, it was never updated) on top of a Snapdragon 800 CPU. You can also use it as a standard projector with the HDMI input or Miracast functionality. It has a microSD card slot, a 6,300mAh battery, and works as a hotspot.