I went down the Wal-Mart road about 2 years ago. 1/4 mile from home on my first ride the chain slipped under heavy pedaling. From that moment on I stopped trusting the bike. I was always a little anxious riding it. Eventually I shelved it. I just recently got a new bike from my LBS. I am already happier I paid a little extra cash to get a bike I feel I can trust. I have had no problems. It's been less than 100 miles so far but like I said earlier. The Wally bike was giving issues after 1/4 mile. It never stayed adjusted.

Find a good bike in your price range from Craigslist or LBS and go with it that way. The big box store bikes are just trouble.