LAs have to pay when the nearest available state school is more than 3 miles away. I would think it’s more common in counties with lots of rural areas.
I live in a (mostly) rural county. The most recent figures I could find (without trawling through the county council's budget line by line) was £6.7m, and that was back in 2009!
Even though we have a large secondary school in the town where I live, it isn't big enough to accommodate all the secondary age children and can't be enlarged because it's bounded by a railway line, a river and privately owned land, much of which is protected by a covenant. Children that can't get places at the local school are bussed to 2 village secondaries, both over 3 miles away.
It must be even worse in the very rural areas.