Stay out of the emergency room. There isn't much you can do if your dog waits until after office hours to become seriously ill or injured, but when it's not a true emergency, avoid emergency animal centers. You can't always control who you fall in love with, but if you can, try to steer your affections in the directions of a less expensive breed. Pedigreed dogs are subject to more than 300 genetically transmitted abnormalities. Go to the library and read about different breeds before you make up your mind about the kind of dog you want.
Puppies require frequent vaccinations, as well as lots of time and attention to train properly.
Bigger is more expensive. Big dogs also cost more to board and groom and medicate. In addition, you get the satisfaction of saving a pooch from a very bleak future. Otherwise, buy from a breeder. If you don't want to go to the pound, go to a breeder.