White vinegar (5 cents/oz) will green clean glass and mirrors. Add a quarter cup of vinegar to a 32-ounce spray bottle, and then fill with distilled water (less than 1 cent/oz), which doesn’t have tap water’s murky-making minerals. Cost: 2.4 cents/40 spritzes.
Spray on and wipe with microfiber cloths, which are washable, reusable, and much less messy than newspaper or paper towels. Your mirrors will be streak-free for significantly less money than if you used a chemical glass cleaner.