3D Printer Technological Recursion
The 3D printer is a good case for technological recursion, and perhaps it can be used as a model for what can be done.
We can take the Simple 3D Printer - a largely printed 3D printer at $160 material cost - to an extreme.
We can use the D3D CNC Circuit Mill as in its current state to produce the extruder. We can use a small induction furnace to make aluminum from scrap, though this is a messy process not recommended for the uninitiated. So you can get stock at $7/foot  of 1/2"x2" bar stock- or $1 per extruder body.
There is no super-simple way to generate aluminum wire, but maybe a desktop induction furnace which eats aluminum cans would be a great idea for recycling. See CEB Press Aluminum Baler
With the Induction Furnace Construction Set, we can do the melt-down - probably in 100 lb volumes so that the process is efficient.
Without induction it is still possible.
Cost is driven down to $140.
We can likely MIG cast the rods - or print rods in hard pastic such as polypropylene or polycarbonate, or simply use EMT tubing for the precision.
To engineer a common-materials 3D printer for high performance is indeed an interesting challenge.
EMT tubes can be reinforced, such as with plaster of paris filler.
Rods for entire printer can go down to $4 for 10' EMT with single tubes for Y axes
Experiments in precision machine design can be made with this simple 3D printer - data measurement, dial indicator, print quality improvement - and contest - $5k prize for science class every year or such.
A dedicated subset could go to Extruder Head design for all types of variations including multi-filament feed into the same head.
- Using the D3D CNC Circuit Mill, we can do the electronics at 1/2 the cost - but lifetime 1/10 the cost as we can fix the board ourselves in that case.