What will affect the cost of the Darien sewer line replacement? What do you need to know about before you consider this service? Of course, one of the first things that you will need to discuss with your contractor is the issue of the cost. There are a lot of people who are often worried about the cost of replacement because things like sewer lines are designed to last a very long time. Therefore, replacing one might be a bit expensive. Discuss your budget with your contractor and then ask them to recommend something acceptable, given your current or expected financial ability.