A fellow custom-school parent, Karina, pointed out a class-size-of-1 school: Fusion Academy.
It seems expensive compared to what we are spending (we are $35/hour, but we are doing the arranging and sometimes provide a room, and this school seems to be $120/hr):
middle school $3,600 per semester per class, 30 sessions.
They say most take at least 6 classes, so $21,600 per semester, or $43,200 per school year. If a session is 1 hour, then that comes to $120/hour
They provide school facilities.
Our custom schooling approach stays less expensive than private schools, and everyone seems happy. But it more hands-on.
Love to know of more class-size-of-1 approaches.