America's carnivores should have no beef with meat prices. According to the National Cattlemen's Association survey of supermarkets in 19 cities, the average price per lb. of six cuts of beef was just $3.12 this month, the lowest level since July. Because the beef supply remains high and wholesale prices are down, many grocers are able to feature meat at significant discounts. Cow-nnoisseurs take note: the six cuts included in the survey are regular and lean ground beef, boneless round steak, boneless top sirloin, T-bone steak and boneless chuck roll roast.