Atom is a very simple and low cost extruder developed in Egypt. It has few parts and it is cut from 3mm plywood. For heating block it uses scrap aluminum plate cut to 20mm x 20mm x 10mm and M6 brass bolt for nozzle.
Here are detailed instructions, files for cutting the plywood and BOM:
http://www.instructables.com/id/simple-low-cost-compact-open-source-extruder-ATOM-/
Parts of the extruder (usual elements such as NEMA 17 motor, fan, thermistor etc....):
This extruder is a part of broader ATOM 3d printer project to bring low cost 3d printing to Egypt and Arab world.
Details can be found at:
https://www.facebook.com/Atom3d.egypt