Get the Walmart bike, just make sure you have your friend or a competent bike mechanic look it over to ensure it was assembled correctly...and to give you some regular maintenance tips.
You gotta look at it this way...a night out on the town, dinner, dancing, etc. would probably cost you what you are spending on this bike. If you get even a couple weeks of enjoyment from the bike, it was probably worth the cost. If you decide you want to get 'serious' (gawd I hate that word) about cycling, you'll have a good idea of what you like and don't like about this bike, as well as a better idea of what kind of riding you want to do, that you can then apply in your search for a new, higher quality bike. If you decide cycling isn't for you, you're only out the cost of a night on the town.
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"Let us hope our weapons are never needed --but do not forget what the common people knew when they demanded the Bill of Rights: An armed citizenry is the first defense, the best defense, and the final defense against tyranny. If guns are outlawed, only the government will have guns. Only the police, the secret police, the military, the hired servants of our rulers. Only the government -- and a few outlaws. I intend to be among the outlaws" - Edward Abbey