Brian, very good estimate. They actually gave an update:

The Kayak measures 16ft 8in [5.08m] long and cost around $500 to make. It is made of ABS plastic, machine screws, brass threaded inserts and a little bit of silicone caulk. That’s it. And it floats. And I can Kayak around in it. In order to print such large, solid sections of Kayak, I had to modify my home-built, large scale 3D printer to print the parts inside a heated chamber so they would not warp or crack
As for it being worth printing, no it is not worth it right now, but within a few years who knows. A typical kayak in this style can be purchased for about $400:
http://www.saferwholesale.com/10-ft-...Fenm7Aod6noAkA