what does it cost to replace rotors

If the brakes are grinding you will need rotors for sure. It's possible the calipers are damaged as well depending on how long it's been metal to metal. It's best to stop driving the car and call for a tow. For an estimate the shop will need to inspect the vehicle but if you want to get a ball park from a shop near you, use this link. https://repairpal.com/estimator Alex