I’ve actually looking into this before. It is very expensive, but it seems like it would a lot of fun. A good site to look at it is http://www.freighterworld.com
It looks like you can get from New York to Georgia, but not the gulf coast.
I read this on the plane from NH. I would have much preferred this mode of travel to flying, but I’m not sure of the likelihood of getting from New England to the Gulf Coast via ship.
To be honest, navigating all the way down the east coast, around Florida and up into the Gulf of Mexico would almost be quicker than flying Delta.