Well, it depends. Regular expenses like food and shots, toys, etc are not terribly big. But I do think that if you take on a pet, you do need to be prepared that there may be something like a surgery that could be a big cost. Our 2 year old lab needed knee surgery, and it was $1200. He is our pet and a part of our family, and we took on the responsiblity of caring for him, so we paid it. He's as good as new. Sometimes vets will allow payment plans; sometimes they will not. I was fortunate that I had savings and could pay for his care out of pocket, but I would have put it on credit if necessary and paid it off over time.
If you do take on a pet, the best thing you can do for them is to take good care of them. Feed them quality food, make sure they receive immunizations and things like flea/heartworm medication, keep them at a healthy weight and get them exercise, groom them properly, treat small medical stuff before it becomes a big problem, and keep them leashed and safe inside your yard. These things will hopefully give them a good long quality life - but sometimes things happen, and pets do need more extensive medical care. Everyone has to make a decision for themselves, but if I were of the mind that I would not be willing to pay for potentially necessary medical treatment - especially for a young dog who could be restored to health - then I would not get one. As someone else mentioned, there are pet insurance plans out there. I have not been impressed really with any that I have seen based on the premiums and how little they actually seem to cover, but I have not researched extensively. Some people swear by them; I prefer just to try to keep a solid emergency fund so that I can take care of a problem if it arises.
We pay about $20/month on food for our lab. Shots and such are not terribly expensive in our area and when all is well, medical expenses do not cost more than $100/year for us - we do not live in an area with fleas or heartworm and really only need basic shots and veterinary visits. He is a strong chewer and his toys need to be durable, which tend to be more expensive - we probably spend about $50/year on things like Kongs for our two labs. We also give him glucosamine supplements because of his knee, and that costs about $50 a year.
Start-up costs also include things like a good collar and leash, a name tag, pet registration, spay/neuter (anywhere from $80-150 in my area), pet bed, good food/water dishes, grooming tools, possibly a crate if you get a puppy and need to train, or if you travel, or if you want a place for the dog to sleep at night, etc.
It's not a terrible burden, but it depends on how tight your budget is currently, whether or not you're willing to allocate some additional funds for your pet, and how you feel about the potential for some larger medical expenses if they become necessary. They sound like (and are) a lot of fun, but so many pets end up in shelters because people are unprepared or unwilling to put in the time, effort, and expense that they do create. My lab is like a child to me and I wouldn't change a thing; I consider him worth every penny, but it's not right for everyone.
ETA - if you do determine that a pet doesn't fit into your budget, but are still longing to have one - maybe time volunteering a local animal shelter would be good? You can walk dogs, pet kitties, etc, but you're not ultimately responsible for any medical bills unless you choose to adopt one into your home. Alternately you can foster animals until they are adopted, I believe, depending on different shelter policies. It might be worth looking into.
You don't even want to know how much that cost. Yike!
