Macy's is banking on Madonna and child bringing in teenagers on a budget with a new line that recalls the 1980s' leather and lace. Tagged Material Girl, it will include clothing, shoes, jewelry, handbags and other categories and will be priced less than $40 on average, reports Stephanie Clifford. While Macy's execs maintain that Madonna, 51, still resonates with today's teens, retail analysts wonder whether she or any celebrity can turn around weak consumer spending. "A lot of times, celebrities' brand equity can wane at the drop of a hat, so making a true long-term investment in …