If I were staying that long I would certainly contact them and ask them what they can offer you.

I've just searched from here:

https://www.marriott.com/search/findHotels.mi and selected government rate and it has several starting from $199 a night.

So you may be in luck.

As for advice - have a search not just on this forum but there is a Hawaii forum. We used it a lot when we went there. I woudl definately try and visit some of the other islands whilst you are there too.