First and foremost there are quite a few lakes in the State of Georgia. Can you expound just a little on your locale? Lake Lanier has varying price ranges - but 5M to 10M is pretty broad. You are obviously working with a property that will have little or no comps - location will determine if you can pull it off.
Proximity to Atlanta etc. is important as well. Please give a little more information - I'd love to get my teeth into this one - sounds quite challenging!