biking in Hawaii

[forum*rider]

This summer my family is going to take a trip to Hawaii and we were planning to either rent some bikes. We are going to be riding in Oahu and I am looking for intermediate biking trails. by "intermediate" I mean fairly easy because my younger sisters are going along and they are 7 and 8 years old. My mom would like to see some nice scenery(waterfalls and forest, some riding on the coas would be nice too) while me and my dad want to ride on some dirt. Can anyone suggest some trails or guides? The guides would have to be fairly cheap. All the guided tours I have looked at are $60 and over, and paying $60 each for 6 people is alot of money.

thanks for all the help :)