When when buying an unregistered car, the car is then registered from current. If you let that registration lapse then you are paying the fee. When registering you may be required to show proof of sales tax or pay the sales tax there
Your vehicle must be inspected for safety before registering, however you should ideally be towing the vehicle for it to be inspected.
Bring the vehicle with your own registration with insurance proof to blue sheet for the safety. This will allow you to get your plates. Head over to the DMV get your plates and put them on the car. The inspection safety check station finishes your safety check.
It can be a bit tricky but you must show proof of insurance to register the vehicle, and you must have a safety inspection for your plates to drive the vehicle. Best case will be your DMV is close to your inspection station of choice.
Quoted from the DMV site itself with hyperlinks for ease of use for you:
"When registering your vehicle at the motor vehicle office, you will be required to pay certain fees, typically as follows:
- The registration fee, which varies depending on the manufacturer's model year or the vehicle's total weight. The motor vehicle office at each county determines the fees. So you need to contact the relevant office to get the exact amount. The county of Honolulu has an online calculator.
- Title application fee. Depending on the county, the title application fee is usually $28 or $33.
There may be additional fees when you register, depending on your county. Contact the relevant office
of the required county for the specific requirements.
RENEWING YOUR VEHICLE REGISTRATION
Owners of motor vehicles in Hawaii are required to renew their vehicle registration annually, and can do so in person, or by mail or on line in some counties. See our Registration Renewal section
for complete details."