Pet's aren't cheap.
There, I said it. If your bottom-line goal is to save the most money, a pet won't do it for you. Now that we've gotten that out of the way, there are legitimate reasons for wanting a pet- as for me, I'm a serious dog lover, and have wanted one of my very own since I was a kid. But I waited. I wanted to be a responsible dog owner- and end up with the right dog. Here's some things to take into consideration:
Do I have means to take good care of a pet?
I'm not just talking about money. Do I have room for the pet to be able to get the exercise he needs to be physically healthy? Do I have time to spend with the pet (if it needs it- Fish, not so much) so it can be well socialized and "emotionally" healthy? Do I have space in the budget to care for the pet should it get sick? Am I willing to feed and care for the pet with its best interest in mind, rather than my convenience?
We waited until we were sure we had room for a bigger dog, because we knew we wanted a large breed. I held out getting a dog until we had a house and a yard- to be fair to our future dog & his health. When we got our dog, he was being fed the cheapest food in the store, but I did my research and settled on a good, nutritious food that was more expensive but not out of the budget. I knew our time constraints- we worked full time so couldn't housetrain a puppy very well, so I knew we needed to find an older dog. When we did get the dog, I spent a significant amount of time on training, as an "investment" for the future.
Where will I get the pet?
For some pets, like rodents and fish, you may think your only option is the pet store. Before defaulting to a pet store, so look to see if any are being put up for adoption on craigslist or Petfinder. You'll be surprised what's out there.
For a dog or cat, you'll have more options- but do your research. Know where pet-store puppies come from, and refuse to support puppy mills that overbreed their dogs in less-than-humane conditions. (Personally, I refuse to even shop for supplies at pet stores that sell puppies, to avoid "voting with my dollar" and giving them any business at all) If you know you want a dog you can take to dog shows, look into a reputable breeder by visiting the American Kennel Club site. Again, do your research, ask the right questions , and expect to spend hundreds of dollars.
But what if you don't demand a dog with a regal bloodline, and just want a home companion and frisbee partner? This is where most pet owners fall. Search Petfinder for the right match in a local shelter, or keep watch on your local craigslist or Freecycle group (some local Freecycles don't allow pet postings). Doing this will give an otherwise-unwanted dog (or cat) a loving home- yours! If enough people get pets from shelters rather than commercial breeding, pets will end up better-cared-for, and pet owners will be better informed.
We got our dog by watching craigslist for the breed we had decided upon. We ended up getting the dog plus supplies for free from a couple that no longer had time or room for him. He needed socialization and serious training, but the work paid off. Had we bought him as a puppy, we would have spent hundreds of dollars at a breeder, because he is obviously purebred. As it is, some owner in his past did spend the money, then decided he didn't want him. We were our dog's third home in his year-and-a-half of life, and we'll be his Forever Home!
In a way, caring for a pet- whether it be a hermit crab or a hamster or a horse- is caring for God's creation, albeit a small corner of it. Supporting responsible breeding and pet care is a way to honor the animal life that God created.