Brake fluid absorbs moisture so after a while they will start rusting from the inside. Changing all your brake fluid every few years will help prevent the rusting.
I had a '91 Camry that had a rusted brake line. Got in one day and stepped on the brake, went to the floor. I saw a puddle of fluid on the ground next to the wheel. I jacked it up and sure enough, the line was rusted. That was pretty good service for a 29 year old car with the original fluid. I never changed it.
I took it to my repair shop and the estimate was $800, which included replacing brake calipers where the bleeder screw had seized and rusted fuel lines.
The car sat so close to the ground I could barely get under it. The brake lines ran in channels near and under the gas tank on that side. It was going to be a LOT of work. The car was worth $300, I had gotten my money's worth out of it so I donated it to Goodwill.
I replaced brake lines on my boat trailer. I got the right sized brake line and a flare tool kit off Amazon. There was very little bending of the lines so I didn't need a special tool for that. It was going to be a lot worse to do the car. I loved that car and seriously considered it for a few days before letting go.
I would have them repair the brake line and also change the brake fluid. If it were easy enough to reach the bad line and if you are handy at doing mechanical things you might consider doing it yourself. If you have AAA you can get them to tow it to a repair shop if you mess it up, or give up. I've been down that road too.