I had to deal with rusting, leaking brake lines for the last few months. Bought all of the parts needed to replace them myself. Ended up taking it to a shop instead, as I didn't feel like ****ing with going through the sub-frame. They charged me $400 for labor. Others have had it done for as little as 250. It's not an impossible task by any means, but it's not the easiest to do on our cars. If you're not confident you can do it, you might be better served taking it to a professional, as having working brakes is kind of a big deal.
Another thing to note that my mechanic talked about: The fuel lines run right next to the brake lines. If they are also rusting, you need to be careful, as you could damage the fuel line and have to replace those as well.