It is of course not really free of costs, the payment is just indirect via the ad budget included in the prizes of products people buy. And the costs are pooled, which share of the costs an individual user pays depends on his consumer behavior.

"freie Medien" et al are idiomatic. "frei" still subsumes "kostenlos" in the general case (e.g. free entry). English has "gratis" or "free of charge", too.

Wait is "gratis" an actual, common English word? As a Spaniard I thought it was a joke kind of thing or used in extreme cases to differentiate, but that it was not really used in English (it is a common word in Spanish).

Similar to "libre".

It is extremely uncommon in British, Australian, and American English (as any search engine will show).

Its not uncommon in my experience as a native speaker. I feel like the context of gratis is more transactional than the context of free; eg. "Its a free country" makes more sense than "Its a gratis country".

Yeah, "gratis" literaly means "free of charge". If you ever see a "gratis country" let me know (;

Because that's not how gratis is used. In analogy to "persona non grata", that would be "America is an acceptable country". It may be gratuitous or gracious, however.