I've done a couple paddles loosely based on Rizetti's ideas. I use a foam (pink insulation foam) blank for the shaft, round in the center and tapered to an oval at the grip area. I put two pieces of table-wetted 4" X ~11 oz carbon uni on the sides (which makes a double layer/overlap along the strength axis), then milk a dry, lightweight sleeve over the uni. Use a c-clamp at each end of the sleeve, hang one end from the ceiling, and add a bunch of clamps to the bottom as weights. Old school style, wet the sleeve with a chip brush, and aggressively pull and push the sleeve with your double-gloved hands, massaging the epoxy into the weave and using the web of your thumb to squeegee excess epoxy away. Let cure, lightly sand, and add paddle blades about as Sam does, again with insulation foam as the core/mold. The shaft will be smooth enough to use with one more coat of epoxy.

My kayak touring paddles have come in at 19 and 20 oz, and if you've never played with a light, buoyant-blade design, they're an absolute treat. Carefully sourced, the materials are in the $30-40 range.