Actually, prime rib is a bit of a misnomer, as less than 2% of all American beef is graded prime. Most of that grade goes to expensive restaurants, although some specialty butcher shops carry it as well. Your local grocery stores will carry USDA Choice or Select. If your budget permits, buy USDA Choice because it will be more tender and flavorful.
Your body really benefits from eating beef. Beef ranks as the #3 source of iron which you need to carry oxygen to your muscles to prevent fatigue. It also provides zinc to improve your immune system, B-Complex vitamins to convert food into energy, and protein to promote strength and endurance.