You can expect to be spending $40 to $400 per month in the first year and $25 to $200 per month thereafter. If you buy the fancy food and toys, it will quickly run up your tab. But the bare minimum will neglect things like vet visits and important medication. The size of the dog doesn't make a huge difference in cost. small dog costs mainly $300-$400 just buying them if they are purebred. If you have one already and it is due for it's shots that month the shots would cost around $200. This is not including heartworm pills, flea and tick medicine (collar, liquid), and rabbies shots.