I can't speak to grad student housing, but I used to live in Manoa, and might be able to give some advice...
Thinking about neighborhoods, Manoa can be a little bit expensive. The houses are very nice and there aren't a huge amount of apartment buildings, even of the small variety. It's a pretty safe area as a result, so biking around there shouldn't be a problem (people do it pretty frequently, as far as I recall).
Consider living in Makiki or Moiliili - they border UH pretty closely (the latter more so). Makiki has more reasonably pricing since it's not on the beach and doesn't really offer great views, and it's also just generally a cheaper area (I lived on the border of Manoa and Makiki, so if you have questions about anywhere in that area, send me a message).
Moiliili is where you'll probably find more students, since it's between Waikiki and UH. I'm not sure if, in either case, those are the kinds of apartments or rooms that'll show up on Craigslist too frequently. You might have better luck securing a lower-rent location using a realtor. And, since it's probably a far distance for many of you, you might be able to do the realtor process remotely.
Do note that your UH ID will get you on the city buses for free, and they run frequently. Living in Waikiki is also doable from a distance standpoint, if you want to be in the thick of the tourist industry. Alternatively, it's something to keep in mind if you'd rather live near the beach but cannot afford to: you can always take the bus there very easily.
If you have specific questions about neighborhoods, apartment buildings, or anything like that, feel free to message me. Though I no longer live in Hawaii, tons of my friends do (many in/around UH), so if I don't know the answer, chances are someone I know might Moving there from the mainland can be quite a shock, so gathering information at this point can only help you adjust!