Thank you so much all of you for your valuable advice. I really appreciate it.
So, I was there at the property yesterday and had 3 different companies come over to look at the issue. What happened was that tenants complained about sewer backup to our PM and he sent a plumber. The plumber tried to use his snake to clear the blockage from the vent right outside the front of the house. Not sure how far he went but his snake got stuck badly and he could not retrieve it back. Right now there is no backup in the basement and it was all dry.
Finally, all 3 companies suggested us to excavate and get the snake out. Also, they think the sewer line might be broken so they might have to change the line once they open the ground and look at it.
We got much better quote than 10k but it is still high and there is lot of uncertainty about how far we have to dig and what all different issues we could find once we open the ground.
We are planning to start working on this next week. I will update this thread when I will have more idea about this.
Thank you all again for your advice and time. You all are great.
Harnit