If you are planning a weather balloon or other amateur high altitude project and need a low cost system for tracking and telemetry communications, check out the Tracksoar Open source APRS tracker:
Tracksoar is the smallest lightest open source APRS [Automatic Packet Reporting System] tracker available. It makes tracking weather balloons, model rockets, RC aircraft, and anything else that flies as easy as possible. It is able to report location, altitude, temperature pressure and humidity to the internet once a minute for twelve hours with 2xAA batteries.
Because Tracksoar is open source you can also add your own modules to accommodate custom sensors to meet your specific requirements. By flying Tracksoar on a weather balloon you can reduce the required helium and balloon costs per launch and it can pay for itself with just 2 launches. No other APRS solution offers this level of integration, compact size, and customization.
Additionally all profits from Tracksoar sales go to supporting the Santa Barbara Hackerspace and improving the resources we offer to the community.
The system was designed by the Santa barbara Hackerspace, founded by Mike Bales. They currently have a crowd-funding campaign underway to raise $22,000 to pay for the first production run of the Tracksoar : Tracksoar APRS by mike bales — Kickstarter.
Note that the system requires an amateur radio license to operate.