If they approve your PR status, your son can be local student and no need pay international fee. Usually new immigrant no need to pay just your case is very different. When you apply for PR card later, you need to consult experts to see what good reason you can give to the government. They will question you don't have intention to stay in Canada, they want to know the reason why you gave up the chance in the past.
For public school, the tuition fee for elementary student is depends on where you gonna live when return back to Canada.
Example, if you lived in City of Toronto, it wil under Toronto District School Board, the application fee is $200CAD, full year tuition is $12,500CAD.
For Markham, Richmond Hill, Vau####......etc, it's under York Region District School Board (City of Markham, Richmond Hill, Vau####......etc.) The applicaiton fee is $250CAD, full year tuition is $ 12,000CAD, medical insurance $450CAD.
For City of Brampton, Mississauga, it is under Peel District School Board. The full year tuition is $14,000CAD ($500 admin fee has included), health insurance $540CAD.
Information is available online, good luck to you and your child.