Patch an old concrete floor or pour new
If the old floor sits flat and dry and just has a few thin cracks, it usually doesn't need to come out. When it's sunk, tilted, broken into pieces or wet underneath, that usually points to the ground or the water below it, and patching the top won't reach either one. I'd rather pour new on a proper base than sell you a patch that fails over the same problem.
What shapes the cost of a concrete floor
The biggest pieces are the size of the floor and how much work the ground needs, since digging out soft dirt and packing a new base takes time and material. A vapor barrier under flooring adds a layer, a tight spot the truck can't reach can mean a pump or wheelbarrows, and a cold weather pour needs protection. A plain smooth finish costs less than a decorative one.