Is yet another choice but strictly used refers to addition of an current constituent (that has been lost for the duration of processing for instance). Agree with Jimi that quite possibly the most proper antonym for "free of charge" is "available for sale." But, "obtained" or "priced" could work as https://docs.google.com/spreadsheets/d/e/2PACX-1vThQYloKZWldp-SOKX4OjBXwRfrgWYaDRrLVem32lfKHmI8mCJiHgR2_0HftTtEvIaeLQv1auoUjdAn/pubhtml