Shopping at Walmart is one way to save money, but the best prices are usually at the company's warehouse chain, Sam's Club. Like Costco , which Sam's is modeled after , the retailer charges shoppers a membership fee to access the ultra-low-markup bulk goods. At $50 to get in the door, the annual fee can deter some shoppers: Are the deals really worth it? The question is increasingly important for US households focused on stretching their dollars, a consumer climate that has favored value-