Here is a drone kit designed for developers interested in working on their own obstacle avoidance algorithms. The Parrot SLAM Dunk Drone comes with a stereoscopic camera and various sensors. It supports ROS and can reproduce human vision and generate a map of its environment to measure distances and identify obstacles.
The drone reconstructs its environment in 3D and computes its position in real-time without GPS. The kit is available for under $1000 at this time.