Need help with making teeth whiter?

Im 15 and i just got my braces off and my family doesn't have $30 to go out and buy the crest whitening strips or any kind of whitening strips even though they work really well for me. I looked up on the internat and i found this "Mix 1 teaspoon of baking soda, with a pinch of salt. Add a few drops of vinegar to it to make a paste. Foam up the mixture a little and then brush your teeth with it. Add half a teaspoon of rocksalt to a cup of water. Gargle with this solution every night before going off to sleep." And people say that works but im wondering is it ok? is it safe on your teeth? If you have any better tricks please let me know.