One of the overhead costs of freedom is the maintenance of having a place for being free. Another is to ensure that the citizens of this place have access to the freedoms therein. Unfortunately, the ones shouting ‘Freedom!’ seem to be the ones who want freedom but don’t want to pay for it.
ISTM that the term is primarily used to describe the absence of a foreign occupying force, that–having invaded the US–would prohibit us from speaking out, assembling, travelling, exercising our religion, or worse depending on their ideology.
IOW, the slogan in the OP is referring to costs associated with maintaining a strong military because otherwise we’d get invaded by people who would take away our freedom.
But how realistic is it really, even going back to WWII and/or the Cold War, let alone today, that anyone could pull off an invasion of the US?