It depends on your location. The slab has to be jackhammered and resurfaced. If it's thick enough to begin with. Otherwise, that whole section has to come out and then a new one poured and tied into the rest of the slab. That could cost a couple of hundred dollars from a contractor who already owns the right tools and has done this several times and doesn't run into any unknowns. Or it could cost a couple of thousand if you have someone who has to rent the tools, hasn't done it before, and runs into problems that aren't apparent at first glance..