Unless you get into large boats (28'+), wood is still the hands down winner with regard to strength/stiffness and being lightweight. That is, of course, if you're using good quality marine plywood. Mother nature is still the king (queen).
This applies to using all fiberglass skin or a foam cored. There might be some minor saving if you got into more exotic materials like carbon fiber or kevlar. But that would be quite expensive.
You see around the net some pretty bold claims about how lightweight their hulls are. Many times, that's a bare hull, lightly made, with no rigging or anything to complete the hull. That or they will list the wieght of the hull using carbon/kevlar but list the chopper gunned hull price and forget to mention the lightweight one costs twice as much until you're ready to order.
(now a bit of self promotion).That's not something JEM Watercraft wants to do. We try and provide the best estimate and average builder can obtain. Not something that is flimsy and will break the first time it's handled roughly.
When the design comes out an if someone really truly needs to have an all fiberglass version, I can try and help with that. But it will be a lot of work and take you about twice as long to build it. You basically have to build a mold first and then pop your hull off of that.
...Wife thought I was outside wrestling a bear 
