Rides up Mauna Kea

I'm going to Hawaii in a month, and plan on going to the top of Mauna Kea while I'm there. For a variety of reasons we'd like to drive to the top, which will require 4WD. From everything I've read, the only choices for this are Harper's rental or a variety of private tours which will be more expensive. It seems likely that I'll rent from Harper's, but before setting anything up I wanted to see if anyone knows of other options. Does anyone know of any private individuals that offer rides to the top? Or other ways I might get up?

Thanks for any info you may be able to provide.

Pete
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