How can I whiten my teeth w/o buying anything expensive?

I use Colgate or Auquafina toothpaste (depending on my mom's or dad's house), I floss in the mornings, and occasionally use mouthwash. If I do use mouthwash, It's either listerine or store-brand fry's (again depending on my mom's or dad's house). I cant change what they buy and i'd rather not spend my money. I heard u can use baking soda? Can someone give me ideas.