usually AIB allow you to have an overdraft that is just under your monthly salary. For example, if you get 2,500.00 per month lodged to your account, I can't see why they would not give you 2,000.00 for example. They usually wont sanction more than the monthly income, as it will be more difficult to keep the account in credit (if your salary never covers the OD balance)
Hope this helps!