OpenBTS and Ettus USPR (software defined radios) have made it inexpensive enough for hobbyists to set up cellular base stations at Burningman.

The difference between an open source base station, and a homebuilt stingray in negligible.

While a grand or two's worth of radio hardware and however many weekends/evenings spent getting it all set up and the a software configured is _kind of_ expensive - it's effectively free at criminal org, corporate espionage, or state levels of action.