Where in Hawaii? On Oahu which is where I live you can get a slip at KoOlina but it's pricey- it took us 5+years on a waiting list to get into Ala Wai small boat harbor.
Are you military? if so there are several inexpensive options- but again all with waiting lists if you are buying a boat in Hawaii already where is it now? There are situations where a person buys half the boat and becomes a co-owner just to keep a slip...
You can be a transient for 4 months- you need to contact the boat harbor
and see what the availability is.
This year is problematic as the transpac will be held and slips during that time (july) will be at a premium...
you are welcome to PM me and ask specifics.
Author & Sailor