2001 Ford Cobra Mustang Cobra engine rebuilt

Hello,
I'm in need of help ! I have a 2001 mustang cobra that unfortunately needs engine repairs. It was low on oil, so the engine is now making a loud knocking noise, I want to know if its worth repairing the engine or buy a new one. If repaired how much would I be looking at in parts and in labor? I currently have one quote from a personal mechanic for 4,000 is this a fair price?

Thank you in advance for your answer !