Line is cheap. Fittings are cheap. If you're having to replace the whole line, starting from the front with new bending and adding as you go, you should really only have to make one flare per line.
That being said, the flaring tools you can rent at AutoZone or the like are worthless. I've never been able to get a very good flare with them and have always had to resort to the hydraulic flaring tool which is expensive and I don't know of anywhere that rents one.
At any rate, I can't imagine it being that expensive to get new lines installed. Unless your mechanic is just trying to drag you through the ringer. I don't know how much my shop would charge, but I know it's easy.
Byron hit the nail on the head for as far as the largest expenditures could be. Calipers can get pricey though wheel cylinders are relatively cheap. I've never really worried about wheel cylinders. If I'm replacing my own brake lines in the rear, I've already got new wheel cylinders to go with.
Wheel cylinders are to re-doing rear brake lines as beer is to a bonfire. (As per my opinion.)