If you can replace the sewer line yourself using a rented backhoe and the pipe then the pipe and fittings for the sewer line should cost you around $150.00 to $200.00 and then another $100.00 to $200.00 for the backhoe rental.
So you could replace the sewer line yourself for $300.00 to $500.00 but if you can't do it yourself then you'll need to hire a plumber to do the job of the sewer line replacement.
Cost to hire a plumber to replace a sewer line is between $50.00 to $250.00 per foot depending on the location and the plumber you hire.
To have a plumber replace the sewer line costs between $3,000.00 to $6,000.00 depending on the length and depth of the existing sewer pipes, local rates and the ease of access to the current sewer pipes.