Greetings! ExpressJet on the CRJ side currently has bases in ATL, DFW, and DTW. I think you'd be able to hold DFW immediately, and ATL immediately or within a couple months. Both of those would be on the CRJ-200. ATL or DTW on the CRJ-700 is a bit more senior for First Officers.

Looks like there are around 10 flights a day between ATL-BHM and most are Delta mainline right now, but ExpressJet definitely does that route too. You would get priority for a stand-by seat and the chance to reserve the jumpseat commuting on ExpressJet. Commuting on mainline is definitely harder on a busy route, but looks like there are a lot of flight options.

Hope that answers your question.