Investors interested in stocks from the Retail - Discount Stores sector have probably already heard of Big Lots (BIG) and Costco (COST). But which of these two stocks offers value investors a better bang for their buck right now? We'll need to take a closer look.The best way to find great value stocks is to pair a strong Zacks Rank with an impressive grade in the Value category of our Style Scores system. The proven Zacks Rank emphasizes companies with positive estimate revision trends, and our Style Scores highlight stocks with specific traits.Currently, both Big Lots and Costco are holding a Zacks Rank of # 2 (Buy). The Zacks Rank favors stocks that have recently seen positive revisions to their earnings estimates, so investors should rest assured that both of these companies have improving earnings outlooks. But this is just one factor that value investors are interested in.Value investors analyze a variety of traditional, tried-and-true metrics to help find companies that they believe are undervalued at their current share price levels.The Value category of the Style Scores system identifies undervalued companies by looking at a number of key metrics. These include the long-favored P/E ratio, P/S ratio, earnings yield, cash flow per share, and a variety of other fundamentals that help us determine a company's fair value.BIG currently has a forward P/E ratio of 8.82, while COST has a forward P/E of 39.88. We also note that BIG has a PEG ratio of 0.79. This metric is used similarly to the famous P/E ratio, but the PEG ratio also takes into account the stock's expected earnings growth rate. COST currently has a PEG ratio of 4.37.Another notable valuation metric for BIG is its P/B ratio of 1.68. The P/B ratio is used to compare a stock's market value with its book value, which is defined as total assets minus total liabilities. For comparison, COST has a P/B of 10.84.These metrics, and several others, help BIG earn a Value grade of A, while COST has been given a Value grade of C.Both BIG and COST are impressive stocks with solid earnings outlooks, but based on these valuation figures, we feel that BIG is the superior value option right now. Breakout Biotech Stocks with Triple-Digit Profit Potential The biotech sector is projected to surge beyond $775 billion by 2024 as scientists develop treatments for thousands of diseases. They’re also finding ways to edit the human genome to literally erase our vulnerability to these diseases. Zacks has just released Century of Biology: 7 Biotech Stocks to Buy Right Now to help investors profit from 7 stocks poised for outperformance. Our recent biotech recommendations have produced gains of +50%, +83% and +164% in as little as 2 months. The stocks in this report could perform even better.See these 7 breakthrough stocks now>>Want the latest recommendations from Zacks Investment Research? Today, you can download 7 Best Stocks for the Next 30 Days. Click to get this free report Big Lots, Inc. (BIG): Free Stock Analysis Report Costco Wholesale Corporation (COST): Free Stock Analysis Report To read this article on Zacks.com click here. Zacks Investment Research