Then take this into consideration also, how many of these children/teens are even Catholic or even care about Christ let alone religion in general ? When most parents just want their child to be in a safe environment where there is no gang violence and major drug use, only to find that there might not be gang violence but the drug use an sex is probably just as much as in public schools.
So perhaps people are paying for two things, the ability to learn about the Catholic faith which can not be done in public schools, celebrate mass for those few who are actually Catholic, an probably the biggest part, safety, they do not want their children in a violent school.
There are plenty of support options for those who need financial assitance you just have to know where to look, or at the very least start asking.
Could the cost be better, yes, but until teachers in these private Catholic schools, want to volunteer instead of being paid, then prices will remain if not grow, as long as taxes and bills to keep the ac , electricity, an water running keep going up then there is another reason for prices.
It is all relative.