Hey Norse, I'm originally from Little Rock so I have a feeling for how things go there. A lot of people on here are going to try to tell you to check craigslist but Arkansas craigslist is pretty poor. If you want to buy a used bike and save money your best bet will probably be Fayetteville due to all the college kids. Check on craigslist for Fayetteville ( I know, I know) and the local papers. If you're buying new it would behoove you to drive into a larger city such as Little Rock, Fayetteville, or Russellville to shop. I've never been to Pleasent Hill but most of the Arkansas towns I've been in don't have a real local bike shop. This is all to say don't buy a walmart bike. Good brands are specialized, trek, giant, gary fisher, Kona, etc.
I typically find places like AR's CL will have the best deals, but the worst availability. So you're likely to get a LOT of bike for a little money, but could take a LONG time 'til you find the right bike.
Google maps makes it look like you're in the middle of MTB heaven!