Rule reminder
Final conjunctions (affinché, perché meaning 'so that') and conditional conjunctions (a meno che non, purché, a condizione che, nel caso in cui) always require the subjunctive. 'A meno che' is always followed by 'non' and the subjunctive, even though the meaning is already negative.
I'll agree to the proposal provided that the budget is not exceeded. Which sentence is correct?