If it was permitted, a good portable setup would be this:
http://www.aircraftspruce.com/catalo...cs_skycom1.php
and three of these:
http://www.aircraftspruce.com/catalo...ges/h10_20.php
with some extension cables, for a voice actuated setup. PTT would be additional wiring/cost.
I picked the DC headsets because they're durable. The cheap ones would not last long in the competition environment.