Oculus's original inner ear hedaphone set costs 5800yen(about $50).
I made a cheap headphone with this item
and inner ear headphone.
Make this main part with 3D printer use this stl data.
Solder headphone line to the pin.
Insert the soldered pins and M3 screw to main part.
Polarity of top contact is positive, bottom is ground.
You can olse see my blog site.
Even though it is Japanse site, you can comment in English.