how much does a public school in the US cost for non americans and for americans?

It costs nothing for Americans and Non-Americans alike. Public school is free and funded by tax dollars, which you have to pay in America, no matter if you are a citizen or not. The Supreme Court also ruled in 1982 that even illegal aliens can go to school.

Public schooling up to a high school degree is free for any citizen or resident of the country, and is paid by local and state taxes. You don't pay any money until you go to college. In California a community college is about $25 dollars a unit (or about $400 a semester plus books) for a citizen and $125 a unit for a foreign student. State universities prices vary but in California they start at about $6,000 a year for a state resident. A foreign student or out of state student probably pays about 4 times that.

For Americans, primary and secondary education are paid for out of local tax revenues. Thus, as homes vary in tax evaluation, there is no one number.