1991 Nissan Pathfinder Left Exhaust Manifold Problem

I have a 1991 Nissan Pathfinder 4Dr V6 3.0L SUV and has a 170,000 miles with a left exhaust manifold problem brought to MIDAS to repair it, but during the replacement of the left exhaust manifold one of the studs broke(but was not told), and later found. I returned to MIDAS, and was told that to fix it, the broken stud portion needs reboring which is beyond their competence because their shop is not equip with the necessary tool, and require to dismantle the exhaust from the engine. What should be done? What is the work hour estimate and how much? Is it worth repairing it though it still run at 13 miles per gal?