Two things that I've tried in the past: flying out of other cities and buying two separate tickets.

For example, could you get to ATL or MIA? I know they're far away from TPA, but they're larger markets and you may be able to find a cheaper fare out of those cities. You could also try buying a ticket to HNL, then take a hop to OGG.

Strategy #2: buy a ticket to LAX, then another to OGG.

Of course, both these strategies could cause extra hassles (e.g., buying two separate tickets may give you problems if the first flight is late and causes you to miss the second flight), but you may be able to find a better deal.