Some good answers already.
I have just taken the same step. I was living in London for most of the last 11 years, where I needed to be for regular work / contracting.
But when it came to setting up my own company, I was getting nowhere due to the cost of living, and kept getting tempted back into the contracting market to give my finances a boost so that I could then step back out to give my business a go.
But as a result I never got traction.
A few factors finally collided and came to a head, and decision was made to uproot. I decided to combine family considerations with the business ones; move north where I have family, get away from the London rat-race (I don't need that anymore), and start the business properly, from home, in a new, quiet area.
And.. bingo. Best thing I've ever done.
So I echo one of the above comments - think about your life and where you really want to be. But I would say very much think about living costs. You're going to need time to get traction with your business; the lower your living costs whilst you're doing this, so much the better.
Ideally you want at least 2-3 years of keeping your costs down, so you can keep as much money in the business as possible.
If you can combine your preferred location with the best location for your business (those costs being a factor), then hopefully you'll know where to be.