All in I think the expenses were around $1200 total for the drone and this was like 8 years ago. Not something most would be willing to waste, but with time and effort you could make something now for probably a third the cost.
We also used a similar setup wired into a Jetski that we left attached to an adjacent dock once too. I can only imagine what others are doing ;D
Do your customers actually pay you to break security and then act on what is found? Or are most of them paying you to demonstrate that their security is perfect and then quietly burying results if they don't go that way?
I know DJI uses some communication method built on top of wifi but is it the type that is susceptible to standard wifi based attacks?