I do real well on my walmart bikes and ride them everyday. I did a month long tour on a Walmart bicycle. As long as you can do your own adjustments and maintenance, they will last quite a while. I usually buy a new one or two each year, not because they break down, because I like a new ride every year or so. I then donate the older working bicycle to charity.
BTW: I think the Skyliner is the best of the bunch at Walmart. 99 bucks here also.