I am not comfortable using any cash to buy BTC in Hawaii or in any country. You would have to know the person that you are buying the BTC from, otherwise you could be easily robbed. I have read that you can do a cash exchange using LocalBitcoins.com but that going rates are usually 10% or more than what is posted on most exchanges. I have also read that there have been people who were arrested for engaging in running an unlicensed currency exchange service by exchanging cash for BTC. So, I would be very cautious.