Making 3D printing filament at home for cheap
medium.com
medium.com
Also, this is completely discounting the time spent to set up and maintain the system, which is entirely nontrivial, and leaves out a lot of quality control steps that are important for making and storing high quality filament.
So basically, fun hobby, but it's not "$7.5 per hour at Home".
It's mostly set and forget. You need to change rollers after few 50-60kg run.