The camshaft fell out of my engine?

Okay so I was driving my car home and it started running rough and wouldn't keep running.I had it towed to a local shop and the mechanic said the camshaft fell out.I didn't see the part he was talking about and my brother says thats impossible.I know Im a blonde but I have never ever heard of such a thing.Is this guy just full of bs?The book I saw showed it inside the engine so how can it fall out?He said it will be about 3,000 dollars to fix.I don't have 3,000 dollars.Any thoughts guys?It is a 1971 duster with a 340 whatever that means.