If it's corroded brake lines chances are it's the fixed ones not the flexi's, so you're limited in what you can replace with.
You can get off the shelf ones, but most garage just make their own as they fit them.
If you get off the shelf it can be done DIY, as they are already shaped for the car. Otherwise you would need a pipe (small diameter) bender so you didn't crimp the pipe.
As a guide, I just had 2 replaced on my 300zx, and it was £140 inc labour and new DOT4 brake fluid.