If you want to have a mountain bike, Look on craigslist, you can probably find a few year old GOOD mountain bike (specialized, Trek, Gary fisher, etc) in your price range. I know when I was younger, I would not have wanted skinny tires...Even riding on pavement, I would jump any curb I could find, as I used to mountain bike back then and any obstacle was good practice
These days I mostly only ride flat ground.
You could also look for an early-mid 90's fully rigid mountain bike. They will handle road and light offroad just fine. And they have no suspension to have to upkeep!
edit: I just checked out the Jacksonville, FL Craigslist, there are TONS of older rigid mountain bikes for UNDER $200. Granted you will need a large frame, there are plenty to pick through from what I saw in the first 20 listings
