Approximate repair cost on sunken floor

[John Endicott]

I'm looking at a property that has sunken floor in the middle of the house to the point where it has separated from the interior walls. I've seen this happen before where a pipe from the sink in the kitchen had leaked for years and was neglated. My question is what is involved with a repair of type and approximately what would it cost? From inspection of the outside the exterior Foundation appears to be in good condition without cracks. Looking at the house from the street the Ridgeline on the roof is perfectly straight and none of the exterior of the house appears to be sagging. Asking price is $55k. Comps in the neighborhood go for around $120k and it's located in a nice quiet neighborhood. Then on the market for 400 Days.