fiji off the beaten track and low budget

hi everyone,

4 friends of mine and me are going to fiji for 3 weeks in july. i was wondering if anyone has some advices what islands tovisit and where to stay. we have a low budget and would like to spend our time on a laidback, off the bbeaten track island. we would also prefer to go by ferry, even if it takes us one day, than by plane. i read about the mamucas and yasuwa, and the bula pass but that would be too expensive and too touristy for us i guess. i thought about taveuni, has someone recommendation where to stay, are there cheap hostels? also read about kadavu? but it's very hard to decide as there are so many islands...hope somebody can help.
thanks a lot.