| 'Extrusion' means squeezing out a long shape; extruding a circle gives you a cylinder. Extruded plastic forms include sheets, tubes, and others. Greenhouse glazing made of polycarbonate, or UV-stabilized polyethylene, water pipes for plumbing and irrigation, plastic shapes and sheets are all doable with slight modifications of a basic extruder. The key may be a ram extruder (simple design) with inductive heating, to which various dies are adapted for profiles (extrusion), or molds for shapes (injection molding), or blowers and molds (blow molding).
With these tools, cheap feedstocks can produce very expensive products. For instance, polyethylene resin costs less than 15 cents/lb (at a density of 50 lb/cubic ft (800g/l)). When extruded into panes of Solexx glass, the end product costs $1/square foot ($10.76/m2). This makes the end product about 20 times more valuable than the feedstock. If an extruder is available - combined with the know-how - then localized production of such glazing could probably yield cost predictions of something marginally higher than material costs, under the DIY-flexible enterprise scenario.
The challenge is procuring the know-how for extruder fabrication and material extrusion. The material costs are expected to be around $5k for the machine - structure, hydraulic ram, inductive heating, and die. This is a prime example of market inefficiency - where middlemen, R&D costs, company overhead, competitive waste, and proprietary technique - make the price so much higher than the open source flex fab scenario. The flex fab innovation required here is the fabrication of a generalized device for die extrusion, injection molding, and blow molding in one, where dedicated machines serve each purpose today.