I saw many people interested in inexpensive lidar or radar sensor that is compatible with the Pixhawk, Arduino.
You must have a look at Benewake TFmini LiDAR sensor. Robotshop public price is about $39, and quantity sales have very good discount.
Benewake TFmini LiDAR ranging distance is 12m indoor and 5m outdoor; FOV 4°; Frequency 100Hz; Precision: cm; Anti-ambient light 70k Lux. Very light weight 6g, micro size 42*15*16mm which can be well integrated to any drones/UAV/Robots or other industrial equipments.
TFmini is a single-point micro distance ranging module, this LiDAR is based on TOF (Time of Flight) principle and integrated with unique optical and electrical designs, so as to achieve stable, precise, high sensitivity and high-speed distance detection.
Typical Applications :
See more at http://www.benewake.com/en/tfmini.html
Thank you !