when i try to start my car it sounds like metal scrapin metal real loud

it does it when i try to start it up and it wont stop even when i try to turn it back off and take the key out i have to unplug the battery how much do you think it would cost to get it fixed

To know the costs, it must be determined what the root cause might be. It could be a faulty ignition switch or even the starter solenoid sticking. Begin at the starter. Check for power at the primary starter wire only when the key is in the start position. If power is still being applied when the key is released, check at the ignition switch. Is there any aftermarket alarm or disable devices that could be faulty?