If you are looking for a segment run, you are probably better off flying out of nearby airports like BHM or CHA. Of course, that will add to your total trip time. You can do BHM-ATL-MDW-ATL-BHM for $248 on 12/31. The only cheap segment run I see out of ATL is ATL-DTW-CAK-DTW-ATL for $210 on 12/17. Your main problem is that the week before and after XMAS are very high travel demand dates and fares tend to be quite a bit higher then. Really not the best time to try and find a mileage run.
So I think this is the winner ATL->LAS is $310 RT gets me 3.4K MQMs and it's an afterwork trip. I figure what's another night sleeping on a plane LOL.