Like everyone said, don't worry about what you paid for it. You own it now, so start enjoying it. As for the brakes, if the master looks that bad on the outside, I can't imagine what it looks like on the inside. I posted on your original post. The only real things you need working on your Bronco are safety related. Brakes are the biggest safety item there is. If you don't have the money to spend on a disc - power upgrade, then at least rebuild what you have meaning: New Master, New drums (or turn them if they are in spec.), New wheel cylinders (or rebuild), new bearings while you are at it, and lastly flush the lines before connecting to your new wheel cylinders.
As I suggested before, if funds are limited, hold a Bronco Bretheren Saturday Party with Good Beer and Pizza and you would be amazed at how much can be accomplished in a short period of time. Hell, I wish I lived closer to help.
Chris B.