I agree that delta.com's fares are always high but I have been able to book them through local online travel agencies (in HNL, for me it's PandaOnline) and get much cheaper fares. It might be a regional thing for HNL, but I've been able to get good fares cross country HNL-IAD.
Example 1: 4/5-4/12 HNL-LAX on delta.com = $649.30. Same flights from pandaonline.com = $371.52
Example 2: 4/2-4/5 HNL-IAD on delta.com = $987.91. Same flights from pandaonline.com = $689.74
Maybe someone can help explain why these smaller travel agencies can get better fares than what delta.com offers. I wish for DL to adopt the best fare guarantee like NW.