As you suggest, it really depends on the type of work and experience of the contractor. We see people just out of school doing web design work (pure design and HTML/CSS work - no functionality) at $30/hour. Good PMs and enterprise Java and C# developers with some projects under their belt generally fetch $60 to $85 an hour. Highly experienced software architects fetch a bit more. The rates charged by companies for these people is obviously higher.
There are exceptions such as people working remotely for mainland and Japanese companies that fetch higher rates. Also, some military contracts pay double these rates.
How much you can charge in Hawaii depends entirely on your people skills and your negotiating skills. Since this is a small community, people often just know each other, and if they don't do the kind of work someone is requesting, they can usually pass a referral to a colleague. Also, since this is a small community, any "deal gone sour" can really bite you in the rear for the same reasons.
You can do well here if you find a niche and establish yourself as a reliable provider in that niche. I often find myself passing along requests for Sharepoint designers, High-End Oracle DBAs, and everyday Web 2.0 (.NET) work -- especially since I'm heavily vested in my own startup project at the moment, and won't have time to take on many projects for a while.
$15 to $40/hour is typical for someone just starting out as a general developer. Then as you establish more Trust and Comfort with your repeat clients, you can negotiate for higher rates. Until clients are steadily coming to you, or until you've Networked your way into more lucrative referrals, you'll probably have to compete at entry-level rates just to land some gigs and put food on the table.
Haven't been a contractor in a long time... But even then, it is sad that the rates haven't inproved over the years. As an app dev guy back in the late 90's early 2000's $75/hour pretty standard (at least I thought so).
But I definitely agree with Laurence. If you're good and your clients are happy, you'll get referrals that will have more wiggle room for negotiating.
The type of rate you get is also dependent on the type of contract you sign. Some companies want you to sign as a 1099 net30 or even net45 - if that's the case, then you need to charge more to make sure you're covered for all of the taxes you're going to have to pay. Also, make sure that you add the excise tax to your invoice as you will be required to pay that as well (the excise tax is a separate amount and should not be included in your hourly rate).
If you're working as a contract W2 - then you can probably expect to receive less than a 1099 but you'll at least know that all of your taxes will be taken care of for you and you don't have to worry as much about the tax accounting.
Another factor is the length of the contract - if it's a short term engagement, then I charge more than if it's a long term engagement.
On average, I usually charge between $65 to $75 an hour for contract W2 and between $85 to $100 an hour for 1099.