A friend of mine wrote an article about the financial strain of owning a puppy. She just recently got a pup and the article focuses on how much she has spent: $1,756 in the first three months.
You can read it here: http://thebillfold.com/2012/05/the-economics-of-adopting-a-puppy/
I am not calculating how much I have spent on Theo in his first year of life because I am sure it will only depress me. Though, he is worth every penny and more, I am sure I have spent at least $2000-$3000.
If you rescue a dog, your costs are considerably less because most rescue pups come already with their shots, neutered/spayed, etc. Plus, you get to save a life! I want my next dog to be a rescue.
Check out the article before you think about buying a dog. There are a lot of things you may not have considered. Do your research. Once you get a dog, there is no turning back.