Try RST Engineering's intercom kit.
Works great.
Easy to understand and follow instructions for the novice.
I built mine in 1982.
The 9V battery lasts a long time.
You have audio in/out options.
Jim added the pilot/crew isolate switch a few years back, so the current
version is even better than the one I have.
Two place expandable to four.
Best price to perfomance value available.

Casey Wilson wrote:
Hi all,
I'm in the market for a battery-powered intercom for 2-to-4 headsets.
Sporty's is kind of pricey, and I'm the basic cheap ba....., whatever. In
addition to battery portability, I'd like to have an adapter to go from the
??PL-59 down to the mini-jack plug.
Any suggestions? For the intercom or adapter, that is.
Casey