Ask HN: Help Looking to find the x,y,z coordinates of a point in a room

I need to find the X,Y,Z coordinates in a room. Don't know where to start. As always, the cheaper the better. Thought about wifi or bluetooth marker with 3 detectors in the room for triangulation but that's as far as I can go. I'm thinking the marker in the room should be less than a few dollars to make but the detectors can be much more expensive. The tolerance should be somewhere with in an inch but at this time feet would be helpful. Are there any commercial product that I can use?