They mention in the build guide that the display is sometimes available for $150, that's probably how it gets to around $200. MPU-6050 appears to be about $30, main PCB is claimed to be $5 or so, another $5 for the lens and foam respectively, and $10 for the strap. That'd bring it in at $205 provided you already had the capability to 3D print and solder and didn't factor in the material cost for those. It's unlikely, but you could probably make it happen.

I assume you could downscale the display to like a 1080p version to save costs as well.