TIP: book a 4WD ahead through Lanai’i City Services (808-565-7227) that also runs the cab service, sells piazza, snacks, beach gear, books, etc. Lanai’i is that small! 
A 4WD will run about $140 a day. So if you stay on pavement it's generally cheaper to book a cab that should cost less than $10 to go anywhere. You can arrange pickups too. 

Caution: When on your own, always bring water and snacks as Lanai’s dry dirt roads range from rutted and rotten to impassable. Some even use cell phones to stay in touch.