Wally Mart "bikes" are made with the lowest grade components put together by the lowest grade labor. The bearings may not fail in a week but I have seen more than enough pedals cranks and other parts fall off quickly and plenty of backwards forks and things like that. If they were $25 then maybe yeah not as terrible a deal but spending even $100 on something you basically should overhaul from brand new is silly. Single Speeds are simple bikes but that doesn't change much on anything as quality can still be absolutely terrible and not worth the cheap price. If you are going to be commuting then get a reliable bike with quality parts. If you are worried about price then buy the best bike you can or increase your budget a bit till you can get something that is well above a wally-mart "bike". Generally the less you spend at the start the more you spend overall throughout the life of the bike.

If you are a bargain bin dweller then Bikes Direct sells bikes that are OK enough with old brand names they bought to give some prestige to their generic products. However they are going to be miles ahead of wally-mart not totally quality but not scraping the underside of the barrel. The KiloTT has always been a long time favorite of theirs that many people ride and enjoy. Nothing great but certainly a solid and serviceable bike that you can have some good fun on.