How to whiten your teeth; cheap
You can spend thousands of dollars on cosmetic dentistry and whitening techniques. But for most people just a few dollars, and a few secrets used at home will do the trick.
Whitening toothpastes are not all that effective in reality. For best results simply chew an activated charcoal gelcap and swish it around a few minutes, then brush gently. Spit contents into toilet when finished, as it can stain your sink. You'll notice a difference right away most likely. Repeat the next day, and then make it a practice to do this once weekly (results are not in as to whether this can be damaging to enamel, so brush gently and don't do this too often).
Another helpful method is making a paste of hydrogen peroxide, baking soda, and a dash of salt (optional) to use as a toothpaste about every three days. It's best to do this at night, as teeth may become more porous after a good cleaning and absorb stains from coffee, tea, etc that you consume throughout the day. Always brush very gently, and only use this recipe about once weekly.
For daily use, the new tooth powders made from clay are also very good, and may even restore enamel. Also look into Oil Pulling, it is said to even heal cavities if done correctly and may also restore enamel. Use a good oil like unrefined coconut oil.
Brush morning and night (gently, and in a motion away from gums), and be sure to floss once daily. Flossing helps to remove stains and plaque from between teeth, the hardest place to reach. Swish with water after meals when on the go.