Jonathan Parker suffered sleepless nights and worried himself sick after being forced to set a pound;125,000 deficit budget last year.
"I have no idea how we are going to resolve this because next year's pay settlement looks no better than this," he said. "I spent virtually every night from March to May lying awake worrying, but not any more. What can we do? We have done everything we can but there simply isn't enough money."
Mr Parker hit the headlines last year when he sent 700 pupils home from Edenham high school in Croydon because he could not afford supply cover for sick teachers. His actions saved the school almost pound;2,000.
"It wasn't the sort of publicity any school needs but at least it made people aware of how difficult it is for schools," he said.
Since then a deficit budget has been set in consultation with the local authority. The school used up its pound;58,000 reserves and diverted pound;44,000 of its capital budget, but it was still not enough.
Mr Parker said he does not rely on parents' donations to raise cash because they already pay for schooling through taxation.
The parents' association has raised pound;4,000 in the past few months, which is useful but nowhere near what is needed to put the school back on course.
"While everyone is grateful for what the parents do, there is a moral issue here about families having to fork out to subsidise the state education sector," Mr Parker said. "Quite simply, why should they? They would be perfectly justified in saying that they already pay for their children's education through their taxes."
He added: "I seem to spend a large amount of time bidding for cash from various Government pots. I just wish they would divide up this money equitably and let us decide how it should be spent, instead of making us jump through hoops for a few thousand pounds here and there."