The reason why Church Schools both CofE and RC are funded was when the original Education Act instituted free state education it was the Catholic and Church of England Schools that provided the majority of schooling to the poor at a time when only the rich/ middle classes could afford it.
The churches own the land and those school buildings were taken over and swallowed up into the State Education System we now see today.
The costing would be unheard of and unimaginably expensive which no government of any political persuasion would want to touch/ deal with.
My biggest bug bear as a state teacher is that the catchments of community state schools are so ridiculous small. This in turn creates pockets of wealth areas for those who can afford to move to the street of that school.
The Church schools use diocese or parish so opens it up - I would like to see a school swap! So many Church parents don't get their chosen school and so many non Christian or of other faiths/No faith parents don't get their community school.
It could be like House Swap but School Swap!! silly idea I know.