For $1000, you can get enough parts to build 10 drones. You need the know-how, of course, but that doesn't cost much but a bit of interest.
As a long time builder of flying machines, I've got to say that the commercialization of this hobby in the form of the DJI Phantom and its ilk is really some sort of pity. Building a drone out of parts that are commonly available takes but a little bit of research, some careful attention, a free afternoon or two .. and voila! Flying thing!
You might be surprised at just how easy it is to build a flying plane out of nothing much more than a few bits of cardboard, an old cell-phone battery, a stick or two, an old DVD-drive motor .. until you do it. Then you'll wonder why you spent $1000 on something that is very, very easy to destroy almost immediately.
(Purist: build, fly, crash, build ..)
Maybe a farmer uses them to monitor the state of his crops and even spot treat unhealthy areas without installing a huge static sensor network.
Could also be used for intrusion detection on a large property. A small group of drones could detect and instantly let you know when somebody trespasses on your land. Again, without installing static cameras/sensors.
Search and rescue could be made more effective.
Package delivery.
We're currently working on a project for an environment agency to determine viability / produce a proof of concept for monitoring methane levels over landfills using UAVs.