The cost to have a plumber clear your clogged sewer line ranges from $80.00 to $200.00 depending on how bad the clog is and the length of your sewer main.
I paid $80.00 to have my sewer line cleaned out which was reasonable and now I just own a sewer line cleaning machine that I bought at homedepot which is well worth the cost and I even helped pay for it by helping neighbors clean out their sewer mains.
You can rent them also but sometimes it's best to just a plumber do the messy work if you're not into doing that work.