I got tired of paying an extra $50 to get a zero degree paddle so I started cutting my paddles in half, putting a plastic core piece inside and fiber glassing them back together. Regular fiberglass resin works fine even with carbon fiber paddles. I have been using two of them for over a year and I'm on the river about 275 days a year. It doesn't look as ugly as you'd think.
Another thing you can do, with Werner Paddles at least, is warm up the crease where they glue the two parts together - it's in the center of the paddle if you haven't seen it before - and pull the paddle apart. Let it cool, sand it a little, and re-glue it together at the angle you want.