So there's no open source drone (and I mean quadcopter in this case) already? 3D printers (using lightweight filament), motors, ESCs, a microcontroller running some open code....?
The hardware typically runs https://pixhawk.org/ on 3d printed airframes https://diydrones.com/profiles/blogs/ukraine-s-drone-air-for... or to OP's point, DJI drones flashed with custom firmware