If you have a bicycle coop in your area, go see if they have a good used bike that fits you. You'll probably spend $200 but it'll be a better bike even if it's older.

Assembly is one big problem with Walmart bikes and the other is that they use the cheapest components they can find. I'm not saying don't buy it, but do so with your eyes open. A part that on a higher quality bike would last for a decade may only last a year on the Walmart bike, but that may be long enough for you to decide if commuting is for you or not.

We used to buy Walmart or Target bikes for our kids figuring they only use them for a year or two before they grow out of them, but now we buy used instead.