I don't live in the US, so I never shop in Wal-Mart, but I always believed the general advice to avoid buying bikes from retail chains. They're cheaper, but that's because of their lower quality, and why would want a bike that breaks down constantly until you get rid of it after two years, when better one will last up to ten (or even more; not applicable for really rough cycling, of course)? If you need something budget-friendly, better buy a used bike that came from a good manufacturer in the first place. Of course, you need to mind the quality, so always check before buying and insist on trial period during which you could return the bike and get the money back, but if you're careful, you might get a little used bike that will last you for years.