When you check in for your flight, so if you want an upgrade check in early (At least 2-3 hours ahead of your flight during busy times like Spring Break, Summer, etc.)...they'll have a sign at the ticketing booth with the prices. $300 for mainland-Hawaii flights and $60 for short-haul flights as of last week. Unless you need the room or you have money to burn, it's not worth it. (See my other post about my F experience on AQ.)