Power Steering on a 2002 Chevy Silverado?

My husband's truck has always been in really good working condition but all of a sudden it grinds really loud and is hard to turn. We've come to the conclusion that something is wrong with the power steering pump. We had someone at a car shop tell us that it had a crack in it and the entire thing needed to be replaced. They wanted to charge me upwards of $500 to fix it and $90 to run diagnostics. When I got home I told my husband about what they said was wrong and what needed to be done to fix it. We popped the hood to kind of double check and it still had power steering fluid and 2 months later, the power steering fluid is still there. If it had a crack in it, wouldn't all the fluid leak out and that would cause the terrible sound we hear? Also, since his truck has power steering, driving it around with the power steering out probably isn't a good thing, right? We just want some kind of idea of what could really be wrong so we don't go in there blind and have some clue as to what we're talking about. He leaves for the Marines in 2 months and our 4 year old and I are going to be using his truck since it's paid off so it has to work well! We're saving money for when he leaves so we don't want to shell out $590 if we don't have to. Thank you!