Byrobot’s Petrone is one of the drones with competitive prices about $70.
They offer a document containing Bluetooth LE protocol which can control the drone in Korean.
(https://dronefighters.github.io/Documents/)
So I implement a python package supporting ros and publish it on github.
In my personal opinion, this provides better performance than other public DIY drones like crazyflie with respect to camera quality, flight controlling, etc.