cheapest way to get smoke out of a house?

Cross-breeze first: open windows on opposite sides and put a fan in one facing outwards so it pushes air out. Wash anything fabric you can, curtains, throws, cushion covers. Bowls of white vinegar or baking soda left out overnight soak up a fair bit. If you've got a heating or AC system, change the filter, it keeps recirculating the smell otherwise.