Fair, that sucks.
Though US-Americans should be somewhat used to paying for medical services. Over here it is definitely not common to pay for vaccines. I don't even know how much paying for a COVID booster is and haven't found anything since no one is wondering this.
As a comparison, the HPV vaccines are 480€ if you are 18 or older (which, again, hardly anyone pays/is able to easily afford). I wouldn't be surprised if a COVID booster was like 50€.