To get an idea of your budget without waiting another six months you could signup for an expense-tracking site like mint.com. It will download your transactions from a bank account or credit card, attempt to automatically categorize them, and lay it all out for you in pie charts. It'll go back in time and organize over a year's worth of expenses in a few moments.
Makes it easy to see where it's all going so you can guess what might go up or down after you quit work.
Some people are uncomfortable with giving a 3rd party site access to their info, which I understand. But I'm lazy and don't mind living on the edge, so it's worth it to me. Plus mint.com has had a good track record so far.