Cardboard is not to be sniffed at as a construction material. (Locating my socks in order to pick them up would benefit from an olfactory sensor, though.) Properly formed, cardboard is both strong and cheap. Moreover, erco, it's made from WOOD pulp! But would I invest ten grand in that guy's project? Um ... no.
When I worked for Xerox Research (UK) many years ago, we used Fome-Cor board (http://www.fomecore.net/) for "soft models" of prototype copiers. It could be made quite rigid with suitable bracing, and would be suitable for some robotic applications.
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-Phil