Relativty
An open source VR headset with SteamVR supports for $200
... are still very far from dedicated sensors, however, we believe that the model can be trained and improved by orders of magnitude. We designed an affordable motherboard that runs the Relativty Firmware, it is based on the Atmel SAM3X8E ARM Cortex-M3 processor and uses an MPU-6050 as it’s IMU. The naked PCB and the components to solder on, cost in total about 25 dollars.