Proximity sensor - RFID or similar - Develop the specification

We are looking for a device/system that can detect whether a small FOB device is within a certain range of a machine. A person will have a key FOB or RFID tag on them and a machine will know whether that person has come too close to the machine for safe operation - about 5 to 9 feet away from the machine (1.5 to 3 meters). This is commonly used with automobiles and key FOBS. The automobile senses the presence of the key FOB and allows the driver to unlock and start the car without ever pressing any buttons or inserting a physical key. Just carry the key fob in your pocket and the vehicle knows the keys are present. Starting with the automobile example, my need is much simpler. I don't need encryption or matched keys. This is a "dumb" detection system. When ANY person wearing any of my specific FOB/RFID gets inside the defined zone, the receiver or detector simply sends a discrete output (on/off, yes/no) to drive a 12 volt relay open/closed. We just need to know "Is a person who is wearing the RFID/FOB inside the safe zone?" The machine has 12vdc power (like an automobile). The FOB could be powered by 5 or 12VDC (or it's own button battery), but prefer passive detection if possible. The cost of the receiver/detector should be less than $100, and each FOB/RFID tag should be less than $20. Annual quantity for 2020 is at least 600 receivers, and 1000 FOBs/RFID devices. YOUR TASK IS DEFINED AS FOLLOWS: Help determine the best technologies to use for this system Determine if the budget is reasonable (or too high or to low) write a specification (a few pages at most) for this system in more detail using industry standard terms your reply back to me must include the word "blue" so I know you actually read this far. Suggest USA based companies that might be able to provide such a system or help develop the system.