Is fixing a risk ring expensive? I wanted to buy this vehicle from an individual

What is your question?

This Saturn is in great condition, but it has what their mechanic said a broken risk ring.That it needs to be replaced or a rebuild motor put in.Im trying to determine if it would be ok to buy it at a low price but be able to afford to fix the problem it has.It a makes a sound when you accelerate or are idling it.its not lound.its like a light tapping

What makes this problem better or worse?

When you try to accelerate to pickup speed