Last WDW trip, we did AirTran from DTW. I understand they charge you for all baggage now (at that time we got 2 free). AirTran are famous for switching your flight time s& this happened to us so you have to know when you book to not be 'married' to those times. However, when they try to switch, you have to agree to/acknowledge the change. If you don't liek the new time, call and they can tell you what else is posssible. For us, they put us aon a non-stop from 1 stop because the change didn't allow enough time to change planes with two kids.
Have you checked Southwest? Last I checked them there were several $70 flights & SW don't charge for bags (2 free). If you'r eon their site click on the "low fare calendar". That way you can see their lowest price fare for everyday of the month you'd like to go. Very helpful if your dates are at all flexible.