Dean,
From my experience, first and foremost you decide whether your doing a open or closed ended criuse. That is to say whether you on a sabatical or your chucking everything for an extented period. Beyond that you take the money that you have and divide by the time you'll be out there. Check your route for anchorges using internet, and or cruising guides, etc. Here is a link that will get you started.... http://www.marinamap.com/en/.
In addition I'd get familar with excel and start putting pen to paper on the costs you'll know you have. Fuel (gallons per month), boat insurance, health insurance, food, repairs, communications (cell, sat phone, etc), maintenance (oil changes, anodes, belts, bottom paint,), prop tax, and travel and fun where ever you are. There could be more catagories. Some people really like underwater photography, or scuba diving trips etc. then there is a reserve because stuff happens. It's all personal choices.
I think the key is to get the basics down and see if your expectations are in the ball park of the cash available.
Like Alex is looking into if you have a skill that you can work a little along the way that help boost the cruising kitty. When I was out, a person that could do sail/bimini repair could have made a few bucks.
Hope that helps
Dave