The closest thing you can do is build a machine to cut PET water/juice bottles into plastic strips and form it into filament. I've done this, it's a neat project just for the hell of it but it will never pay off.
the reason filament costs as much as it does is not because plastic is expensive, plastic is cheap but making the filament is complicated and time consuming
@handy333, I wouldn't recommend it. The surface finish isn't going to be nice enough for that, and it's going to be hard to deal with the small detail. Maybe with a resin printer, but you'd need a big resin printer for that.