I took a look at these videos.
Very interesting project, but with the naked eye you can already see some diameter variations and deformations in the extruded filament. So I think it could give poor results in a 3D-printer when using standard nozzles of 0.4mm. Might be okay for 0.8mm, on a direct drive printer (without bowden tube), and if you accept lower quality prints.
In Europe good quality filaments are available from around 20 euro/spool, which sounds reasonable to me (from a European perspective at least).
However, to produce art and as a toy in school to promote recycling of plastic, the injection moulding stuff in these videos is absolutely great. It could teach the kids a lot. So the kids could recycle their empty coke bottles, and produce a nice piece of art with it. This is guaranteed to get their interest. Why didn't we have such things in school?
These's guy's have an extrusion machine, and I think they also have a still experimental setup to extrude filament. Have a look here;
Maybe you should ask on there forums, as on the website I do see the extruder, but not the filament add-on.
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