The problem with matter and antimatter is not the amount of energy you need to expend to get them to come together - the problem is the amount of energy you need to expend to get them to keep them apart.
Both matter and antimatter will happily float around and come into physical contact with each other (including the walls of the container or any air in it), whereupon annihilation will occur spontaneously. To stop this from happening the moment you create any amount of anti-matter, you must devise a way of keeping it away from matter. This is usually done with magnetic bottles. Which require energy.