Why do cinema cameras cost too much?
Look at it from a data rate point of view: a GH4 records 4K at 100 Mbps.  A RED Carbon Fiber WEAPON records at 300MBps.  That's 24x the data rate.  Look at how very much more expensive it is to purchase a CPU that's 10% or 30% faster than "normal" and you might then have some understanding of how much more expensive it is to offer 10x or 30x the performance in a camera body.