Anyway you go it won't be cheap. Forwardair is the least expensive part and should cost less than $100 from Chicago to Atlanta. The expensive part is getting someone to crate it and take it to Forwardair.
Try this, find a MBE (Mail Boxes Etc) near the seller http://mbe.com/ and see what they would charge to put it in an oversized cardboard box on a pallet and deliver it to Fowardair Chicago.
Another option is check with people you know in Atlanta and find out if any of them work for companies that would have trucks coming from Chicago to Atl and see if they would be willing to put the bike on the truck and you pay the driver $100.
Also see if the seller knows of any motorcycle shops or scooter shops in his area that would be willing to prepare it for shipping and use their carrier to ship it. You might get a lower overall cost through them.
Good luck and don't let them get you down, remember Scarlett O'Hare was from Atlanta.