One big advantage Wal-Mart stock offers above Costco is that the entry price is far more attractive. Wal-Mart is currently trading at a price to earnings ratio of 14 times earnings over the last year, a discount versus an average price to earnings ratio around 18 for companies in the S&P 500 index. Costco is much more expensive: The stock carries a price to earnings ratio around 28, a premium versus the broad market and nearly double the valuation currently being assigned to Wal-Mart stock.