They aren't the first to do something like this. Here's a very similar project made in 2007: http://www.natrium42.com/halo/flight2/
Q:How much did it cost? A:The system that is presented is a little over-engineered for historical reasons as well as for future expansion and test purposes. It's possible to build a system for $500 with just a cellphone link and a microcontroller, but make sure that coverage is good where you intend to launch and use a good cellphone antenna.