Wildcard:
Im thinking of doing the bare boat thing. Throw a compressor, some beer and a couple of cuties for a crew on maybe?
I did about 500 dives on Midway when I managed the dive operation up there in '98. That is one of the furthest islands to the NW (1200 from Honolulu) but in between you have Nihoa, Necker, French Frigate Shoals, Laysan, etc, etc.
Great diving along the whole chain. Plenty sharks. You would be quite aways from the next nearest dive vessel (up to 1000+ miles) .
I figure two ways to go about it if you wanted to mount an expedition. A big enough vessel with a compressor. This is the open ocean up there. A center console ain't gonna cut it.
That means you need something that has at least a 1000 mile range, and that is just the closest islands. If you were the crew and captain, you are still looking at well over $1000 a day with no labor involved for the absolute minimum.
Would recommend having everyone dive rebreathers to save on compressor use.
Time. Depending on how far northwest you go, you would need a few weeks. Unless you had a very fast boat and then you would need a few more thousand a day to pay for it.
Which is why mostly only scientists have dived these islands. The only other cheap option is an open ocean capable sailing vessel, two zodiacs (one for backup) and a small compressor, O2 bottles, and rebreathers all the way to save on gas and fuel for the compressor.
Anyone want to take this further than a ipe dream?