I'll give you credit if you sleep in your car overnight--just make sure to find a safe place as there are occasionally rental car break-ins. You'll also likely find the surf to be on the South Shore during that time of year. The winter is when the waves pick up on the North Shore--so don't be too disappointed if the waves are flat to a foot or two.
Not the expert on hostels, but I do know that there's a large concentration of them in Waikiki. If you do end up staying in a hotel and still want to be on the North Shore, the Turtle Bay Resort is something you might look into. Also, camping at designated beach parks overnight requires a permit. More info on that
here.