Kevin and John from the Dis Unplugged podcast recommended Assagio's during their Aualani series. They said its good red sauce Italian (think Chicken Parm, etc) and entrees are priced in the $20 vicinity. They enjoy it and recommend it.
They also recommend Anna Miller's near Pearl Harbor. We ate there this week and it was a good, very casual, and cheap stop. We went in around 4pm and there was no wait. We each had pancakes, got one slice of pie to go, and we had one soda and our bill was $19. Can't beat that in Hawaii!
In the North Shore, we ate at Kono's and LOVED it. It's quick service hole in the wall place with a few picnic tables outside, but the Kalua Pork Bomber was to die for. DH said it was the best thing he ate all trip!