[bobds]

You can probably get a spec-sheet for their proprietary materials if you ask. You might have to reverse-engineer cartridges with security features though.

The Fab@Home guys are trying out various different materials, since their syringe-based extruder allows more flexibility than the RepRap.

http://fabathome.org/wiki/index.php/Fab%40Home:Materials

As far as cheap materials go, it doesn't get much cheaper than garbage plastic.

http://reprap.org/wiki/Recycler

[steveklabnik]

> You can probably get a spec-sheet for their proprietary materials if you ask.

Or you could just go here (this is my old startup): http://marketplace.cloudfab.com/fab_facts (click through for every datasheet on every machine and material)