It depends whether there is diplacement or not. I once owned a property that had a cracked slab caused by a large tree too close to the home. There was no displacement (i.e. the height of the slab on botyh sides of the crack was virtually the same). The crack was about 1/2″ wide and 20 ft long. Cost about $1500 to have epoxy pumped in to fill the crack. The engineer that did the preliminary report and recommended the fix said that virtually every slab in SD County has cracks in it which in andf of itself is not a major issue. When the two sides of the slab on each side of the crack start moving in different directions, that is when the fun begins.