Plumbers took all my mad money. I was mad they took my money but glad they fixed my slab leak. The hot water line developed a leak under the kitchen cabinet. They were here a half day and used a FLIR camera to detect the leak's heat signature in the slab.
I'm sure glad I shut off the water a few hours before they got here because it let the slab cool down and the FLIR worked a lot better because of the temperature difference.
They fixed it with the old up and over technique using PEX. Wishing I had the tools and agility to crawl on my stomach in the attic to save a bit of money but, alas.
I deal with slab leaks all the time for my job and a single line reroute should be under $2000. Unfortunately, I can almost guess which company charged you $4200 for this. If you have a second one that needs to be addressed, I would recommend shopping around for a different plumbing company.
Also, some of this could be covered by your homeowners policy.
PM me if you’d like some additional information or if you have any questions.