Walmart is ok for generic stuff, and you don't have to pay anywhere near $2000 for a mountain bike. There are LOTS of old-school hardtail Trek 820 's on Craigslist. The rigid ones from the 90's handle great and came with dependable parts and wheels.
You can buy brand new mountain bikes with modern stuff for about $400-800 very easily, by checking places like Bikes, Cycling Clothing, Bike Parts & Cycling Gear: Bike Discounts & Deals from Nashbar
, Save Up To 60% Off Road Bikes, Bicycles, Mountain Bikes and Bicycles with Bikesdirect.com, New with full warranties
, or craigslist.