Like you, I can’t vouch for the Salk vax. That was injectable and hurt like the dickens. Us kids got them at the Dr. office and there may or may not have been a fee. The Sabin vax, the sugar cube one was free. I recall that you had to take three doses in three weeks. One sugar cube per week, and no one was charged for any dose. You brought your family to the school, church, or other designated meeting place. You gave your names and you got your cubes. As scouts at the time, we helped with parking lot management so I was there all three weekends. I never saw money change hands.
I was part of the first mass vax. Shots that really hurt. Docs and nurses were in the Gym and kids lined up down the hall in the afternoon. Lucky that our school did not get any of the tainted cutter lab vax. No charge, but parents had to sign a permission slip.