DL has a monopoly on the non-stop's on these routes and thus you can expect traditional legacy pricing with cheaper fares requiring a roundtrip purchase with a Saturday night stay. I'm guessing your trip does not include a Saturday night stay and thus does not qualify for the cheaper fare classes. Also, many cheaper fares have advance purchase requirements -- some might have a 7-day advance, and the cheapest X/V fares may often require 14 or 21 day advance purchase. There are tricks like hidden city where you purchase a one-way OMA-ATL-MCO fare and a return ATL-OMA one-way. These will generally be more than the roundtrip fares with a Saturday night stay, but may be less than a roundtrip without a Saturday night stay. It's also a violation of Delta's ticketing rules, although the general advise is that if you don't do it too frequently they will ignore it. You also assume the risk if there are IRROP's they will re-route you via another hub and you may have to buy a separate ticket to get to ATL.