I externed at Emory, and here's the situation from my short stay:
There are 3, possibly 4 sites that you'll rotate through, so staying in the call room is close to impossible. I dont think that externs normally do it, but I may be wrong. I tried to find some place that was central to all three hospitals (Crawford, Grady, and the Emory Clinic) which will put you close enough so that you'll have a short drive early in the morning when you have to show up at these different hospitals. Google the different hospitals, and find a place that's close. I stayed at the Highland Inn, which was pretty expensive if you don't have the traveler's discount. Some cheaper options that come to mind were the Motel 6, or Super 8. Just make sure that you're not far away because you will be expected to be on time, and traffic can be bad.
Regardless, it's going to be an expensive stay. You have to pay 10 bucks a day for parking, and food. It's worth it, though. They let you help with extractions at Grady, you see some ridiculous surgeries, and the residents are hillarious. You'll learn a lot.