Cracked cast iron plumbing. Owner wants 1k patch job, my plumber wants an 11k total repair.

I’m in contract for a house built in 1908, priced at $129K. During the inspection, we found out the plumbing was leaking, so I had a well-reviewed, reputable plumber check it out. His verdict? The cast iron plumbing stack is cracked and needs to be fully replaced, which will cost $11K.

The issue is that the crack is near the floor, meaning they’ll have to jackhammer up to 10 sq. ft. of concrete to access and fix everything. The toilet, floor drain, and venting are all close together and likely tied in, so those will also need to be redone. The repair includes removing the toilet and a half-wall (which won’t be replaced), supporting the stack, replacing the bottom section with new plumbing, laying gravel, and redoing the concrete. It comes with a 5-year warranty, so while expensive, it’s at least a long-term fix.

The seller had their own plumber come out, but this guy has way fewer reviews and is from two counties away. His solution is a $1,600 patch job—just cutting out the cracked section, swapping in PVC, and tying it back into the existing cast iron. Way cheaper, but I’m worried it’s just a temporary fix that could lead to bigger problems later.

So now I’m stuck trying to figure out my next move. My realtor wants me to reach out to my plumber to get their opinion, but obviously he is going to stick with his quote. I really love the house, but this is a huge unexpected cost, and I don’t want to get stuck with a major issue down the line. What do you think?