<---lives in hawaii
USPS Priority is your best bet, although to and from Hawaii travel time is not guaranteed at 2-3 days, real ship time can vary from 3-7 days, and it is not guaranteed by USPS.
Ground shipment is the cheapest alternative. Although businesses for some insane reason do not offer Ground to Hawaii, it is available. i recommend you go to a Fedex-staffed location to avoid hassles and idiots for this. Rough estimate on ship time for Ground to Hawaii is 2-3 weeks, but you will see the same reasonable prices as to the Mainland.
DO NOT ship anything USPS Media Mail, as things get lost a lot more than average to Hawaii, and ship times can extend into the months.
Avoid USPS First Class as well, You will face ship times comparable to Fedex Ground, at a greater cost.
If you have any specific questions, feel free to PM me
