This past May when I was looking for manifolds for my 1994 5.0 I found them new 3 ways. Cheapest was painted, most expensive was ceramic coated andbthere was another set that had a susposedly special coating that was better than paint but less expensive than ceramic. I went with the painted ones. They were $350 for the pair I believe.
If yours are still good you could just pull them, strip them and have them powder coated. That would probably be less expensive than the $500-$600 new ceramic coated ones would cost and probably outlastbthe boat/engine.