Actually Hawaii was a possesion of the US for many years before it obtained Statehood, and for most of that time ordinary US currency was used.
In 1942, when the possibility of a WW II Japanese invasion of Hawaii was considered a serious threat, the word "HAWAII" in large black letters was overprinted on currency circulating there. The idea was that if the Japanese did successfully invade, the overprinted bills could be demonetized to prevent the Japanese from gathering it up and using it internationally.
At the time the 1935 series was in use, so that is what was overprinted. As an additional security feature, the seals and serial numbers were printed in brown.
I don't collect currency, so I have no opinion on whether the prices at
this website are reasonable.