If you want reliable, the simplest solution is buy a bike store bike, not a Wal-mart bike.
I'm not familiar with bikes and their quality, but I've bought my bikes at @ Walmart and I've been happy. Both were around $100. I still use them both. The one is a mountain bike and the other I take on 25-50 mile rides. Like I say, I'm happy with them and I'm just not a bike person to know the difference. Not sure on how it would do going cross country.
the quick list: weight, durability/reliability, ease of maintenance, assembly quality.
More specifically, the brakes on inexpensive bikes are absolute garbage. The rims are heavier (and possibly steel), the tires are thin and flat-prone. The bottom bracket, headset, and hubs use low quality bearings and you're lucky if they come properly adjusted. The cables are probably not properly adjusted. Bars, stem, seatpost, and saddle are made of inexpensive, heavy materials. The frame is made from cheap, heavy metal, and if it's a mountain bike with with shocks, the pivots and such are going to be far more likely to break than those on a quality bike.
Other than that, there's really no difference!