I shopped around a bit for pricing and this is the reply I got from Scootaround, Inc.
We currently do not service with norwegian cruise lines at the moment they have a contract with care vacations, which you will need to contact them in order to get scooter rentals and pricing, there contact number is 1 877-478-7827, they will be able to provide you with the service you need.
So apparently you HAVE TO
rent from Care Vacations IF
you are cruising with NCL. I'm waiting to hear from them about pricing and will post any info I get from them.