We bought a very inexpensive (<$20) intercom system marketed to motorcyclists on Amazon ... and have actually been quite happy with it. The price has gone up and down but is $18.99 right now. Search for "GSI Super Quality Waterproof, Rider to Rider/Passenger 2 Way Radio, Intercom System." The battery life has been great, we have been able to adjust the volume to hear each other but minimize wind noise. The reviews aren't very positive, but we thought for $20 it has been well worth it.