[Jamwinner]

I used to dabble in model aircraft. A 'drone' is just a computerized one. I could regularly cobble one together for a few hundred, most of that being electronics. The body was balsa wood with shrink film covering, super cheap. Not everything has to be titanium and carbon fiber. Nowdays, the electronics are cheaper than ever, and can be strapped to many homebuilt craft with little issue. This all ignores vto style crafts, which I am unaware of. The hard part is training your control system, but once calibrated decently you are good to go.

The problem is the bar of effort. Bombs are even easier to build, yet few with the will to build one for nefarious purposes seems to be effective in doing so, even with provided materials (without training, see IEDs). Same with guns, tanks and other complex items. Anyone can make a gun from hardware store items, but most criminals will steal one instead. The impulsive instinct that drives most crime seems a burden on complex tasks.

[pasabagi]

I'm not much of a chemist, but I don't think bombs are particularly easy to build. I do a bit of metal plate etching, and I've found multiple times that useful chemicals (specifically nitric acid and hydrogen peroxide) are pretty tricky to get hold of, because assholes use them to make bombs.

I had a friend who was making black powder as a schoolkid, and he actually had the police turning up at his house to ask questions about his purchasing history - which is a small sample, but it fits with the basic intuition about how you'd stop people from building bombs: make non-household bomb-making stuff impossible to get hold as a private individual, then just monitor people that make weird purchases of the chemicals that remain.