From The Guardian, some useful suggestions for side businesses you could set up to help finance a career change.
Watch your mind as you read - it will say things like:
1. I've read all this sort of stuff before
2. That's fine for someone else, but not me
3. I could never do that
4. I would look like a fool / cheap / a failure
See if you can notice those thoughts, thank your mind for its input and go deeper into the option. If you can find something that allows you to cling on financially, one of these options could help you make your escape plan work and help you find freedom.