When I was leveling Cooking and my wife was leveling Alchemy I found that something I could make helped her out. I would make Sliced Sardines and use my Carbon Rod to fish up Cobalt Jellyfish in Port Bastok. Now, it isn't 100% all the time but I found that I got them at a pretty decent rate. If you can fish for the sardines (Bastore in Port Windy) and make them into Sardines (level 10 Cooking I think) then you might be able to do it cheaply. Of course, this would be time consuming.
Also, check this site out for all your fishing needs:
http://www.clanwind.com/ffxi/fishing/default.asp