Foundation Issue

[Zachary Phelan]

I recently negotiated a contract on a house for 70k and it retails around 125k-130k. The seller had to discuss the offer with his sister, it was an inherited property. When I walked the house the second time while he was on the phone with his sister I found foundation cracks in the garage, driveway, brick in the house. It was build it 2003 and it settled in 05. After getting off the phone with his sister, he said, she wanted to remind me of the foundation issue..... His mom ended up suing the builder for 20k, because the tile in the kitchen kept cracking. There is a crack in the master through into the kitchen. He told me where the crack is after the negotiation process. 

Looking back I should of renegotiated on the spot, but I didn't. I am no foundation expert, but I will be after this transaction. My question is how much does this sound like it is going to cost? I have a few contractors going out there and they all say they cant take it at the price I am selling for. I have considered hiring a engineer to get me a quote, but dont really want to shell out the $350 bucks. The good news is the seller is realistic and understanding, so when I go back to him I should be able to renegotiate. I just want to go about this the right way. 

Any Thoughts or feedback would be great. Thanks all and have a Grateful day!!