As Katie mentioned, Craigslist is a great resource for student housing. Be aware that there are many old-style plantation houses that are available for rent to students, so don't limit yourself to apartments only as you search. Many of these older homes have either separate "ohana" units or separate upstairs and downstairs entrances and are perfect for college rentals. (My boyfriend and I live in one of these older homes and have been renting out our upstairs for the last few years--the arrangement has been perfect, since we spend part of the week on the Kohala coast and need help caring for pets, etc. when we are away.)
There is also a page on the University site that lists off-campus rentals: http://www.uhh.hawaii.edu/housing/offcampus/
Best of luck to you as you prepare for your move to Hilo!
Cynthia Hoskins, R(S)
Clark Realty Corporation
Are you looking to buy or to rent a 3 BR place? Hilo has some of the best priced real estate in Hawaii and if you buy a 3 BR house and rent out rooms to other students, you could end up with very little of the mortgage to pay yourself. However, many of the homes in Hilo are older and a professional inspection would be quite important.
Cindy Siok, Realtor
Altera Real Estate