You could always reduce this cost by flying small cameras on a rubbish bag, especially a £35 near infra-red HD video camera: www.armadale.org.uk/balloonphotography.htm In many applications, image resolution is not critical.
In a light wind, the line can be let out and the balloon released on the windward side of your site of interest. But, here again, buildings can cause turbulence.
I would like to add that trying to attach a normal camera and rig to a balloon set-up can present its own problems.
I have been known to fly delta style kites in very tight areas. These have been surrounded by trees, large trenches dug in the ground or around buildings. I would not recommend flying under these conditions unless you really know what you are doing and then it can be potentially dangerous. Buildings or standing structures can create updrafts of swirling air that can destabilise a kite quite easily.
In really tight or unsafe areas, I would suggest a pole or mast for safety.
Now we have entered a different realm altogether. These machines definitely have their place and that is in the hands of an experienced controller (in fact it should be two operators in case of failure). Yes, a quad or similar remote control device is ideal for built up areas, but again have their own problems. You need to be well versed with the craft and be able to fly it under different conditions. It should have a fail safe system to help bring it home if there is a problem (thats if you remember to turn it on). The battery life is generally short lived, whilst a kite/balloon system can potentially remain in the air for hours. The props on a quad are dangerous and can lacerate down to the bone if they connect with soft tissue. I could go on, but they do have their merits. They can be flown indoors and up close in areas where other technologies cannot enter. We do have quadcopters amongst our arsenal of airborne platforms and I have even built my own custom system that has GPS, waypoint logging and other lovely additions for the like minded techno nerds to glean over. Personally, I prefer the relative safety and enjoyment of kites as the primary lifting element.