It's sell by the quantity of material so you have to design the parts with the less material possible.
The White is the cheapest of all.
The quality is good and the finish (For the white) is a bit textured.
You can see that it was a powder that has been use.
Here is the list of materialhttp://www.shapeways.com/materials
the complete set of parts on for the MiniHEX is 126$
Lot of parts and the top canopy is 30$ alone.