Nothing is free, at all, in the sense you apparently mean. The costs may be hidden, but they always exist. So what people are using here is a colloquial sense

Nothing is free, at all, in the sense you apparently mean. The costs may be hidden, but they always exist. So what people are using here is a colloquial sense of the word free. When you walk into the doctor's office to have something checked out, you don't run the risk of having a large bill just for the privilege of seeing a doctor. If you get hospitalized, you don't run the risk of being bankrupted just because your job is too shitty to provide you with health insurance. Free in the sense of not a huge amount out of pocket at time of service and not going to financially cripple you to make extensive use of.