You could make the first two blade halves with just a couple layers of fiberglass to make sure everything is shaped and matches up nicely with the blades assembled back to back and then go for the real lay-up. Back a couple of years ago when carbon fiber was really hard to get, I made a GP with four layers of 10 oz. fiberglass. I think it was around 32 oz., which is plenty light, but it had a lot of flex, sort of like western red cedar. I really think carbon fiber is the way to go, because it is so strong. A good paddle is really important, so I don't mind putting some time and money into one.