What are symptoms of bad rack & pinion & power steer

Toyota Camry LE 1999 130,000K 4cyl 2.2 What are the symptoms of the need to replace the rack & pinion and/or power steering pump vs replacing the pump alone? I'm experiencing intermittant difficulty steering and returniing steering wheel back to straight position left or right. Had a mechanic friend (not boyfriend) test drive only and he barely felt problem (naturally!). I was with him, so I saw that he did not have the full experience that I do---some days worse than others. He suggested the rack & pinion/power steering pump might be the problem, but would only know if it actually went out. I'm a single mom and cannot afford such an overwhelming expense all at once. How long can I drive it like this? And how can I know for sure this is the problem in case I wanted to buy a part at a time at eAutopartstore, then have my friend do the repair? Your expert advice is appreciated very much. Thanks.