Yeah it will be $500, to match it will have to be poured from a truck, not a bag, around here a yard is $160, whether you need the whole thing or not, it will take a couple hours to get old out and a couple boards for new.....truck charge for concrete and delivery fee for small order.......$500 is a cheap fix. Then you have to stand there and wait for it to flash so you can broom it.
I would want my old concrete pressure washed to match the new 4x4.......
Its your fault(they work for you), you will have to pay for it, I would let it be a lesson learned and get back to work,
bucket trucks will break 3" of concrete in a hurry if there loaded and its hollow underneath, you can guess how I know.