There are several choices for extruder head. The most obvious choice for us would be the Makerbot StepStruder MK7. This is not out of the question. The price is reasonable at $199 and it seem to be well designed. It is however presently out of stock which would delay this project. Another choice is the extruder from the UP! Personal Portable 3D Printer. This extruder seem very simple in design and I was also able to locate decent teardown photos After looking at these images we are contemplating building our own version of this head.