NO, You can not compute the “COST” of anything provided for by the government as you can not compute what the tax payers would have done with the very real resources otherwise. Cost is an individual value. It can not be determined when government at the point of a gun steals property from one person a tax payer and gives it to another person in the educational bureaucracy.
You can however determine a numeric value of the education of the average person. You will not get within plus or minus 40% as there is no accurate way to assign all the inputs of stolen wealth into the education bureaucracy. There are hidden bureaucracies sending money to education systems. Then the education systems work with law enforcement, social services, engineering etc so their additions must be accounted for. Then there are volunteers whose time would be sold for money otherwise.
A few school districts will put out numbers on the monetary costs of the school, sometimes even with per child done for you. My own district does that reporting: $5,542 per child per year, though that will go down in the next school year because of budget cuts. (Have you ever noticed that the first cuts are in schools, police, and the like, and they never start with welfare or salaries?)
In his series on public compulsory schooling, John Stossel referenced figures of $11,000 per student minmum going as high as ~$27,000 per student in certain areas, like DC.
The TRUE COST of government schools is much higher than government tries to tell you. The government is lying as usual. They leave out things such as pension costs and costs of school buildings.
Or invest it and retire early. The idea of general education for financial purposes is stupid regardless of who dispenses it. Specific vocational training is far more efficient and you can save so much that you can get contingency training and still make off like a bandit compared to trying be a Leninist superhuman.