very loud engine rattle noise
 

2004 Galant v6 97,000 mi. very loud engine rattling noise. I don't believe it is the valves as I have read about in here, but I could be mistaken. I had it diagnosed by a local mechanic and he said it was the ?? bearings(crank I assume) and the engine needed replaced at $4-5,000. How can I be sure if it is the bearings or something else that could be fixed easier? thanks in advance for any help.