It would be pretty difficult to obtain one since they are only found in Hawaii and aren't available on the market. The NRCC has them, but only will sell them for educational purposes. Plus they don't make that great of pets, they're nocturnal and only live for 3-11 months and about 90% of the time they'll be buried under the sand.
I have seen they once on the market and where going for $200 each and where marked as cuttlefish. I fell sorry for the person who purchased them, because they probably lived about a month or two before they died.