When you mean “each” the expression is “apiece”: these pizzas are really cheap—only ten dollars apiece.” But when “piece” actually refers to a piece of something, the required two-word expression is “a piece ”: “This pizza is really expensive—they sell it by the slice for ten dollars a piece.”

Despite misspellings in popular music, the expression is not “down the road apiece”; it’s “down the road a piece.”

List of errors