Are you in New York? Contact Marshall at the River Connection in Hyde Park and see if he has any trade-ins that might fit your friend. He mentioned in another thread that he may have a customer trading in a Venture Islay 14, good medium paddler sized seaworthy kayak. New they are around $1000 but this one is used.
It is possible to find decent sea kayaks for $300 to $500 if you are patient and persistent, though more difficult in high population areas where you will have more and quicker competition for low priced boats. You have to be ready to offer cash and a quick pickup when the ads appear.