I don’t think challenging this action as a tax would work. The government would argue that you don’t ever have to pay a red cent of that money if you don’t get a passport. They’ll further argue that sex offenders are intentionally dissuaded legally from obtaining a passport. That’s the whole idea; to make the process expensive and dangerous. There’s no guarantee how the authorities in another country would react to seeing someone branded as a child molester. I guarantee you no registrant in this country would ever be allowed to travel to countries where it is easy to have sexual contact with little kids and any real threat of action from law enforcement is absent.