^ tojayho, those are different sized bikes. do a little research on rules of thumb for your height/inseam and bike tubing lengths (top tube and seat tube).
you can often roughly determine bike size by looking at its head tube.
i just checked atlanta craigs, and there's very little there. at this high demand time of year, deals are going to be hard to find. if i were you, i would search the bikeforums and ebay.