The average total main sewer line replacement cost. Main sewer line replacement cost in the outer boroughs typically has a range of from $8,000.00 to $12,000.00. However main sewer line replacement cost can vary based on other factors.1  If a tree or trees are present in the sidewalk area a Parks Department Permit.he average total main sewer line replacement cost. Main sewer line replacement cost in the outer boroughs typically has a range of from $8,000.00 to $12,000.00. However main sewer line replacement cost can vary based on other factors.