You can buy telephony wire that is way cheaper, I dunno why that guy is using speaker wire.
In SHTF you can steal the wire from the public network also.
I just found a chinesse pair of phones for 20 bucks, they say they support a wire up to 200 meters
Chinesse intercomThat intercom works with 4 AA batteries, you can adapt it to work out of 12V.
I think is the same model the guy in the video is using.
Also, don't forget that you can use a signal amplifier if you need a longer wire.
Maybe I'll get a set to do some experiments