Intercoms that mount into the helmets are expensive because ones that work well aren't simple. Wind resistance, VOX, noise cancellation, and interconnection are all serious engineering challenges. When you're done with that, the user wants to integrate CB radio and stereo music!
It has a lot in common with aircraft headsets, so you might look into some used or reconditioned avionics equipment. It won't be cheap either.
Asking us to work your problem through email or PM is a disservice to the rest of the readers who would not benefit from the work that's normally shared in the forums.