I just put a lot of effort into a 2000 model-year Mazda that's in perfect condition, but REEKED of cig. smoke. Cleaning EVERYTHING you can get to, from head liner to the underside of seats will make a big difference.
Changing the filters in the AC also made a huge difference. When you aren't using a deodorizer/vinegar/ etc., keep the windows open. If you spray the interior with Fabreeze (spelling?)/ etc., keep the windows closed for a day or two.
After about two months of effort, the smell has basically gone.
Someone recently recommended leaving containers of vanilla extract in the car.
Good Luck!