Rusted steel hardines - HELP

My son has a 98 ML320 that was given to him by a friend. The steel fuel lines going to the rear of the vehicle are both badly rusted and have leaks in several spots. We want to get them both replaced to be on the safe side . I've done some research online and here on the forums. From what I've found each line just be around $85 and already prefabricated to fit into the vehicle.

My question is....where would be the best place to purchase the parts from and then how long should it take for such a repair? I've called around and am getting varied costs. I just want to know what's involved so that I can be educated to make the right choice.

Thanks all!!