What is the opposite of free as in "free of charge" (when we speak about prices)? We can add not for negation, but I am looking for a single word.
I don't think there's any difference in meaning, although "free of charges" is much less common than "free of charge". Regarding your second question about context: given that English normally likes to adopt the shortest phrasing possible, the longer form "free of charge" can be used as a means of drawing attention to the lack of demand for ...
The fact that it was well-established long before OP's 1930s movies is attested by this sentence in the Transactions of the Annual Meeting from the South Carolina Bar Association, 1886 And to-day, “free white and twenty-one,” that slang phrase, is no longer broad enough to include the voters in this country.
For example, imagine some food company decides to make their fruits permanently free. Online, you can "order" them (for free), but in person, what do you do? What would be the professiona...