Are you IN Columbus? Are there any other airports you'd be willing to fly from? And when are your dates?
Last year we flew from Pittsburgh to Orlando for $110 each including taxes by catching a fare sale. I know these sorts of fare sales happen quite a bit from Pittsburgh. I don't think we've ever paid more than $150 r/t since taking over vacation planning ourselves the past 7 or 8 years. We've never flown SW since they just started flying out of Pittsburgh last month, but the other airlines have always been very competitive for that PIT-MCO route, so don't rule out other airlines.
$600 for 5 people might really be pushing it. You'd have to be VERY persistant. I mean check a few times a week, if not daily, for those fare sales to hit. I wouldn't rely on JUST Ding fares. I would check every airline.
I've mentioned this many times on these boards, but it's worth repeating because it always works for me. Most fares bottom out (pretty much any fare I've ever checked) about 8 weeks before departure date. I start checking daily at about week 10. Some have taken til week 6. Most drops happen in the overnight Tuesday into Wednesday, but that's not always the case. I go to Travelocity and check the flexible dates for my month. It'll bring up a list of fares, cheapest first and by carrier. When prices appeal to me, I go down the line and see which ones have availibilty for my dates. When I find flights I like, I go to the airline's website and book there, saving that extra $5 or whatever Travelocity charges you to book. This method has never failed me. It's how I got the $110 fare to Orlando. And I managed to snag a R/T with just one layover (best you can do from Pittsburgh) flying into Rome just days before Easter (and consequently a week and a half before the Pope died. . . so you know they were charging top dollar for those seats by then) for $393 including taxes and fees!!!