I'm sure if you divided overall spend by the number of pupils, the cost may even be higher than £6k. I was thinking more along the lines of, how much money would a state school receive in additional funding if you were to send your son there? And therefore how much is the LEA saving by not having to provide that funding?
Its criminal that so much of the ring-fenced Dedicated Schools Grant from the DCSF ends up being retained centrally by the council (this isn't a dig at OMBC, it happens everwhere). Cut down on the middle men and get the money into the classroom! Then we might have state schools which can compete with private schools in terms of the quality of education they provide.