Although there's a certain awe-inspiring beauty to the images that hobbyists' weather balloons can capture from the edge of space, in fact most of the good stuff happens much nearer the ground.
These flights can be broken into three phases. The first, with cool imagery of the ground below, lasts about 10 seconds. In the second, the balloon starts to swing around wildly in the wind, and you get a long period of nausea-inducing footage. Finally, the balloon ruptures, transmitting a quicker but equally queasy view as it plummets earthward.
Since most of the interesting images come in the first 100 meters, why go higher? Besides, by keeping the balloon low, you can control the pan and zoom, rather than trusting to dumb luck.
Setting up a balloon for low-altitude observation involves some interesting logistical issues, but it isn't particularly difficult. To begin with, balloon flight is all about payload weight. The more you want to carry, the more lift you'll need, meaning a bigger balloon and more helium. In the United States, there's a practical limit to both: FAA Part 101 regulates what size and type of balloon can be operated without notifying the FAA prior to flight. Moored balloons can't have an inflated diameter of more than 6 feet (1.8 meters) or a capacity of more than 115 cubic feet (3256 liters). These requirements will pretty much drive all the other decisions you make.
The best source I've been able to find is Balloons Direct. It sells a US $35 chloroprene weather balloon with a 1.7-meter diameter and a total fill capacity of 2464 L—enough to lift 2.1 kilograms. I ordered two, just to be safe.
Next I needed a payload. There are lots of pan-zoom-tilt webcams around, but most require an Ethernet connection, which would leave little lift for the camera—an altitude of 30 meters would require an entire kilogram's worth of Cat 5 cable. I turned my attention to Wi-Fi–enabled webcams, settling on the Vivtek PZ7131. It features 640-by-480 resolution, a 2x optical zoom, and a wince-inspiring $340 price tag.
The camera required about 1.5 amperes at 12 volts. I could have used lithium-ion batteries, but because I had to tether it anyway, I decided to run 12 V up on a wire from the ground, using the power line as the mooring line as well. I spent an evening with my 15-year-old son braiding a 30-meter length of two-conductor wire out of some 22-gauge single-conductor wire and splicing it between a jack and a spare 12-V power cube. The lift penalty was well under half a kilo. A test confirmed that the camera received enough power to operate, so I was set.