Repairing or replacing stamped concrete
If your stamped slab is sound but the color has gone flat or water no longer beads on it, a reseal usually brings it back. That's the normal upkeep, and the FAQ below covers it. It's different when the slab is cracked through, sunk or heaved because the ground under it settled. A patch won't hold on that and won't match the rest, so I'd rather replace the section or the whole slab on a properly packed base.
What sets the cost of stamped concrete
The biggest pieces are the size of the area, how much digging and base work it needs, the pattern and number of colors, and the sealer. When the budget gets tight, people usually want to trim the base first because nobody sees it once it's poured. That's the one place I won't cut, because a nice pattern on settling dirt cracks just like a plain slab. A simpler pattern or a single color is a better place to save.