I have run across lots of sailboats for free, all needed work but many were seaworthy and just needed a lot of TLC. I have seen many on Craig's list, it just takes time to find them. There was one fantastic 30' Norwegian folk boat with all the new equipment, sails, rebuilt diesel and hardward ready to put together. The owner had to move it out of dry storage and had no time for it, was willing to give it to anyone who would finish it. I found one totally seaworthy 23' minicursier in great shape for just paying the back slip fees, the owner had moved to another state and was willing to give it away to stop the monthly slip fees from getting higher.
Par is right, keep your eyes open for abandoned projects or hulls that are neglected. Get one with a trailer so it will not cost you anything when you are not using it. Another good place is to go to any larger boat yard, there will always be abandon projects that the yard had to seize for back fees. Often they will sell them cheap, or even free, just to free up the space.
Wood boats are more maintenance (and more likely you will find one cheap), but the material costs are less and you can get by with hardware store quality finish and adhesives if you are storing it covered out of the water. Fiberglass hulls of course are much lower maintenance, but usually heavier, and major repairs use much more costly materials.
Good luck on your search, finding partially restored projects that has been abandon is your best bet.