Anyone know of any low cost museums or interesting attractions in Altanta?

I am flying standby to Atlanta on Thursday for an exhibit over the weekend. If I get there early enough I will have time to kill.

I will be taking Marta so where ever it is must be within a couple of miles of a Marta station.

What my hope is would be to find points of interest such as art museums, historical exhibits or any other interesting areas that preferably are real easy on the wallet.

Where is your favorite place to hang out in Atlanta?