That's not going to be hard to find at all, but you should probably enlist the help of a real estate agent to help you find good neighborhoods. I'd recommend staying on the South side since it sounds like driving to the Mother-in-laws is going to be high on the priority list. Peachtree City has a lot of character and probably has a lot of what you're looking for as far as night-life outside of Atlanta. Traffic is going to kill you though, a 30 minute drive from the North side of town to PC can easily turn into an hour and a half drive.
I like Lake Allatoona more and more each year. If you are anywhere on the Northwest side of Atlanta, it's a short hop to be on the water there. Roswell, Marietta, Alpharetta are all nice places up there. Lanier is also beautiful now that the water level is to full pool. Jackson Lake tends to be muddy but it has it's great spots.
Lake Spivey in the Stockbridge/Jonesboro area is also nice, but probably on the high end of your price range. It's also private, but its not hard to meet folks on the lake.
You might want to check out this neighborhood in Gwinnett county (East side of Atlanta): http://www.norrislakega.org/
You can find homes around the lake for very inexpensive, but you have to be on the water or know someone on the water to use the lake.