The cost to clean a clogged main sewer line can vary from location to location.
But when I had my main sewer line unclogged last summer it cost me $80.00 including the service fee.
The plumber came out and ran an auger machine down the main sewer line which shredded what was in the sewer line and unclogged it.
Call some local plumbers and they should be able to let you know what they charge but it shouldn't be more than $100.00 to $150.00 to clean the main sewer line out.