It's true, if you live off campus you'll need a car. The housing is expensive all around OC, and ewurgler is correct that Santa Ana/Tustin is going to be your best bet for affordable housing. Keep in mind, though, that some parts of Santa Ana are very sketchy. Orange County isn't very good about public transportation either, but there are bus routes that take you to UCI, so if you move off campus and don't have a car, I would check the OCTA website (http://www.octa.net/schedules_maps.aspx) to see if you live near a UCI bus route.