Gesture controllers provide developers with the ability to create unique interfaces to their embedded product that allows the user to interact with their device in a hands-free way.
Gesture technology can vary quite dramatically in its capabilities and the technology that drives it. For example, a low-end system can take advantage of an infrared light-emitting diode (IR LED) and a photodiode with a cost of less than $10, whereas a higher-end system, such as Leap or the discontinued Microsoft Kinect, might cost several hundred dollars. High-end solutions often use several cameras, including an IR camera, to capture motion and then break it down into a gesture.
For most readers, integrating Leap, or another gesture controller that is typically USB-based, is going to be outside your price range and will also require quite a bit of development time...