When a brake line becomes overridden with rust, the main option is to repair brake lines with new ones in a total replacement. Some drivers, who feel that the rust is not too bad, will opt to repair just a section of the brake lines, the brake line hoses, or the brakes themselves instead of the entire piece of equipment. The majority of mechanics or automotive specialists out there will strongly recommend replacing the entire brake hose line to make sure the vehicle continues to run smoothly and with no dangerous side effects. A full replacement can cost a couple of hundred dollars.
For more info, see How to Repair a Rusted Brake Line