cheapest way to take off deodorant stains?

Depends which kind of stain. White marks on dark clothes: rub the fabric against itself or with a dry nylon sock, it usually just brushes off. Yellow pit stains on whites: make a paste of baking soda, hydrogen peroxide and a little dish soap, scrub it in, leave it an hour, then wash. Avoid chlorine bleach on those, it can react with the aluminium in antiperspirant and make the yellow darker.