Brake line question.

[Apparition]

Hey guys, this is my situation.

I recently had to brake hard and it was working then the pedal hit the floor. However, it then goes back up (master cylinder is ok). So I eventually got it home. Next day, lots of brake fluid all over the driveway. So I decided to check the lines, refilled some brake fluid and pumped the brakes to find out where the leak was. Well, its the right front brake line. But its rusted out bad. It's the line that runs from the master cylinder, across the firewall, down the chassis and into the wheel well. Right where it meets the firewall/chassis is where it effectively squirts me in the face.

Question is, how hard is it to replace this specific line? Is this little beast expensive?

What are stainless steel braided lines? Is that like the whole line from the cylinder to the brake itself?

Thanks for the help.