Here are some things I know, slightly related to this context:
I know several movies (big hollywood stuff) have fallen back to using what are basically souped-up RC Helicopters w/ good cameras mounted to them as a low-budget alternative to full-blown aerial photography. The results are good, and its way cheaper than a manned helicopter.
I know that flying even unmodified RC Helicopters is really friggin hard. You will crash and destroy a lot of equipment learning the basics. Also, this is not a hobby for people who work with their hands. You will cut up your hands at some point. Surgeons, pianists, etc. need not apply.
I know that flying RC planes is much easier, but it'll be harder to get nice slow overflights, etc. unless you've built something really special.
Some really good stuff here.
I do (or did) fly RC Airplanes, and dabled in small RC Helicopters. Actually, I got into the helicopters with the exact idea that this thread is about. Using them as a platform for photography of outdoor sports.
The reality is, exactly as posted here. They're really friggen hard. First of all, as you can see, those small lightweight easy to fly setups are way too unstable, shaky, and poor quality cameras. The other thing they're not really saying is, you probably can't fly them if there's any kind of wind. I know with the small electric helicopters, unless it's dead calm, forget about it. They just get blown away. I know, I've tried.
To get good results, this really needs to be done with a larger RC helicopter, probably gas powered. A 60 or 90 size. So what you're looking at is upwards of $2000 for the airframe and radio, not including the camera. Then, you have to know, that learning, flying, and maintaining something like this is a full time hobby in itself. You can't do this, while *also* doing overland travel. It's just not something you dable in.
Airplanes are easier to fly, but you generally need an improved airstrip. Typically, about 200 feet of grass. There are some STOL airplanes... really any airplane can be STOL. With a big enough engine, they can take off vertical out of your hand. The problem is the landings. A really skilled pilot could probably stick a landing on 50 feet of runway, reliably. The problem with airplanes, is they have to keep moving forward. You'd have to take a series of swooping shots. Maybe it could work for stills, but forget video. You could probably build a large, slow flying plane, and aim the camera sideways, and hover around the site. But you won't find anything suitable pre-built. So now you're designing and building from scratch. Full-time hobby again.
Also note that, it's extremely easy to crash these things. A gust of wind on landing, radio glitch, or a dead engine, could take out the aircraft, and the camera. So significant financial risk as well.
There are a number of ready-made systems available. But notice... "surveillance" is one thing. Actually getting high-quality images, is a whole other matter.
