Personally, the Fernbank isn't worth the money. DS7 was bored with it. Tellus is great. axast5 - if you have the money, I would go for the UGA &/or Emory programs. For other programs, you may want to try looking at Atlanta Parent Online. They list all types of summer programs by region.
DS7's school does Kid Chess, which is awesome! We are lucky b/c his current school offers a lot of extra programs (like he's also in the Black History Program), which feeds his need to learn new things.
I assume by GAT, you mean Target? Target is a great program, but it doesn't focus necessarily on core academics. DS7 is in 2nd, and he is learning about the heart right now. Last semester it was about criminology.
We are on the lower end of the income bracket, and DS7, I don't think, doesn't qualify for DYS. You may want to look into getting involved with your county or the state gifted association (I give good advice, but I'm horrible about taking it - I am not a member of either - AAACK).
Good luck to you!