My Cavalier had developed a rattle under the.

My cavalier had developed a rattle under the hood, that was diagnosed as a water pump going out. I put it in the garage with the intention of having the water pump and timing chain replaced. But both were still good and mechanic suggested the tensioner and replaced that but it didn't stop the noise which is like a bearing going out type sound. I had just had the oil sensor plug replaced a week before. My car is only worth about 600.00. How much of the trail and error repair am I responsible for if it is not fixed? And what else could be the cause of the sound which was originally diagnosed as water pump going out.