Finally a cost puzzle, and my first (nontrivial) (hopefully) minimum primary!! This puzzle was full of little tricks: finding a workable layout, realizing that I would need an auxiliary atom in the center that would later need to be removed, and managing waste (+2 metallicity per product, *just* small enough to clear before running out of space). I know these things are second nature to more experienced alchemists, but I had fun figuring it all out. This is my favorite solve so far! :3

(This solution was made possible by omclone.)