I shipped a car from the east coast and paid around $2k but it included being flat bed truck driven to the west coast for the boat ride over.

Hawaii police will issue a warning if you don't update DMV records beyond the month it needs to be registered locally. And then after than 30 days, you can run into trouble. Although I know people who have been on-island with mainland plates for 6 months + and no one notices/cares.

So if you're planning to visit for up to 2 months and can do without your vehicle for the ocean journey to/from the islands, shipping a car is far cheaper than renting one right now for longer stays. And there's no tax/insurance implications. (Although if you lease your car, your lessor may have an issue with it moving off the mainland for a bit.) If I was visiting for 2+ weeks and could do without a car during the shipping time, I'd totally ship my car than deal with the car rental crisis that exists this year.