In February I flew from CMH to HNL. I found the cheapest fare was to fly CMH-LAX on Southwest, then fly LAX-HNL on United. It cost me $288 for the CMH-LAX round trip on Southwest and $300 LAX-HNL round trip.... That's obviously sub $600.

The one thing I would caution is if you check a bag, you would have to pick up your checked bag in LAX then recheck it and go back through security. I met my wife out there so I only needed a carry-on (I packed some items in her luggage so I didn't have to worry about a checked bag).

You can also do an overnight in LAX which can help mitigate the trip (it is roughly 12 hours from when you step on the plane in CMH and when you step off the plane in HNL or KOA for that matter... assuming you don't have a really long layover, it is obviously longer if you get stuck with a long layover).