Stinger's cost ~38k and are not guaranteed to work so multiply that by the probability of failure.

You can buy drone control system can cost below 1,500$ ex: http://www.micropilot.com/products-mp1028g.htm, granted there are good reasons to buy / build something far more expensive but we are looking at low cost baseline. After that it's a question of range and payload for 10,000$ you can get an RC jet that can do 200 mph and carry a camcorder for surveillance. Call it 15k for a fairly respectable surveillance aircraft. As to being able to fight back just add a spike.

PS: Now figure out what you can do with say 10 billion$ aka 600,000 of these things. Worse yet that's just an opening, they are cheap enough that you have plenty of budget for other things.