You can't buy a mountain bike for $200 new. You might find a used one on craigs list that will be 100% better than settling for a cheap wal-mart bike. I found a 2005 specialized hardrock comp on craigs list for $50 bux. The kid had it all srewed up, but I fixed it for $0 and 2 hours of my time. Look for Specialized, Gary Fisher, Trek, Jamis, cannondale, diamondback, GT, Iron Horse....And the list goes on. You also need to find out what size bike you need. Walmart bikes are one size fits all...
Do not buy a cheap mongoose or schwinn !!! You will hate it later.