Comment by KingOfCoders

I think in some way it has become that, but I assume the roots are different. People might have said "Freier Eintritt" before it became associated with money. One might be able to see this in "Portofrei" which does not mean "free as in beer" but no postage required - for my feeling it doesn't feel like "Freier Eintritt" yet, it does not have as much money connotations (though when it wanders to the front like in "freiporto" it feels more to be about money).

I do think there is a spectrum. Funny things like "Freifahrt" or even "Freifahrtschein", or "Freikarte", or "Freiexemplar", "Freiparken", "Freiminuten" or "Freivolumen" (people might use "Inklusivvolumen") - so I'd argue when used as part to form a new word it is a synonym for "kostenfrei" (not yet in "Freiwild" which changed a lot).