The expenses you should expect when buying a dog are expenses that never really end. You can buy a dog inexpensively thru the humane society, or the pound, or you can pay more for one from a pet store or a specific breeder.
What comes afterward are the vet visits for shots, spaying or neutering and occasional check ups to ensure your pet remains healthy. You may seek guidance from the vet on the right kind of food to feed the new member of the family. Additional items to purchase would be food and water bowls and a bed for them to sleep in.
You would need to consider what flea treatment to use. Again, your vet should be able to provide you will several options, then you can decide which one to use. If you have a long hair breed, you may want to consider professional grooming, unless you can do it yourself, which requires a bit of patience.
It's important to be prepared for these costs in the interest of the pet being adopted. All in all, dogs are a wonderful addition to a family and earn your love early on. They are great protection, company and they offer unconditional love.