Most calls start with a surface that's flaking, pitted, stained or patched so many times it no longer looks like one slab. A new top fixes the look and gives you a sound surface to walk on, but only when the concrete under it is solid. If it isn't, the same wear tends to show through again, which is why your slab gets a close look first.
The price moves with the size of the area, how much loose concrete has to come out, how many cracks need repair and how many edges, steps and drains need handwork. The schedule turns on that same prep, the product's cure time and the weather on the day. Because this work usually takes a crew and sometimes a permit, it's a job for a licensed contractor, and your written estimate spells out the price and the prep.