Thanks for the asnwers guys!
I asked this because a discussion developed in an Israeli aviation forum,and someone said that an adapter between helicopter and fixed wings headphones plugs costs about 50 bucks, and I'm currently making audio cables adapters,like 3.5 mm plug to 1/4 inch plug or male to male 3.5 mm plug,and the costs of the components combined doesn't get to 10 bucks, so I was interested why does the adapters costs so much.