$2.3 billion -- That's what first lady Michelle Obama said consumers have saved on fresh fruits and vegetables, whole grain products and other healthy foods purchased at Walmart stores over the last two years. Responding to her call to make sure healthy foods don't cost more than less-healthy alternatives, Walmart lowered the cost of the good stuff and, Obama said Thursday, increased sales of fresh produce at the stores. This disproved the conventional wisdom that healthy products just don't sell. Apparently they do, if the price is right.