Take a look at the Motorola Talkabout with a VOX headset. The MS350R version is waterproof or so they claim. The headsets are probably not but they are cheep. My wife and I use them when doing long bike rides so that we can carry on a normal conversations and she can warn me to slow down or speed up. Seems like she is always warning me about something. They claim a 35 mile range but we never get more than a mile apart. That's when I tell her to slow down. :-)

http://www.amazon.com/Motorola-MS350R-35-Mile-Talkabout-Waterproof/dp/B004PGM9PO

KT