I understand the idea of getting a Wally World bike. Mine is from Target, but after just 18 months, I'd say I've changed at least half the components on the bike. The cost of that adds up over time, too. That's one of the reasons why you'll be advised to steer clear.

+1 on Craigslist. We BF members will usually gladly evaluate CL bikes you're looking at as best we can if you post a link here.

I also advise avoiding suspension forks if you get a new bike from the dept. store. I have one. It's cheap, heavy, and can't be locked out. hate it. One of my next projects with my bike is to spend $ to replace the suspension fork w/ a rigid fork.

Other ideas:
*Is there a bike co-op in your area? They may have rehabilitated bikes for sale cheaper than you could get at a dept. store.
*Some for-profit bike shops also carry used bikes and may be able to help you find something inside your price range on a used bike they have kicking around...

All the more reason not to shop there. A bike shop or co-op will be able to give you advice, answer questions, etc., etc. You won't find that at X-Mart. You also won't get $hit for after-purchase service.

Some of the bikes at Target, etc., have a few halfway decent components. My Schwinn, e.g., came w/ Shimano shifters and rear derailleur. There are occasionally diamonds in the rough there, but if you don't know what to look for you're playing with fire.