Depends entirely on the size, age, health, and tendencies of the dog, as well as where you live.
Our dog is a 40# lab mix, around 3 or so, and in good health. She goes through a 50# bag of dog chow about every 3 months or so. I believe those bags are around $15 at Wallie World, so that’s about $60 a year for kibble. She also gets biscuits and rawhides once in a while, to the tune of maybe $20 a year. These expenses can go up fast if you have a larger dog, or one who needs special food. (A lot of prescription food is a buck a can.)
Dolly’s not prone to ear infections, bladder infections, joint or skin problems, or impacted anal glands or worms. This means she only has vet visits for routine vaccines and testing and accidents. At the clinic where I used to work, a yearly checkup with vaccines and heartworm test was $105, plus $30-60 for a year of heartworm prevention. We were in a high-parvo area, too, so we reccommended parvo boosters at the six-month mark, too, at $20. Routine care: $165 a year for a 40# dog (without flea prevention).
She also got stung or bitten a couple of times by something venomous, and on another occasion got into my seizure medication. Exam fees were $30 a visit (rechecks for the same problem are less), plus antibiotics, steroids, and inducing vomiting. All that would add up to about a $100-$120 a year for Dolly but can really get high for some pets.
Then we have various dog accoutrements that are hard to calculate on a per-year basis. Leashes, collars, bowls, brushes, shampoo, a kennel, that sort of thing. These costs vary wildly by what exactly you buy and how often you have to replace it. For Dolly, I’ve had to replace a few bowls (we finally just switched to stainless steel), a couple of collars she sawed through (long story), and a leash. Total start-up and replacement costs on that stuff so far: ~ $100 over a year and a half, but $60 of it was for a crate.
Then we have toys, which are indispensible. Again, costs vary wildly with what you get and how rough the dog is on her stuff (and how many toys you buy). Remember, a bored dog is often a destructive dog, which will cost you more in the long run that a well-stocked toy box.
Then we run into replacing things the pet has chewed up or peed on, which can be minimized with crate training and lots of toys. This expense is totally dependent on the individual animal.
You’ll go through a lot more vaccuum bags and other cleaning supplies, and there’s the extra time and energy devoted to walks, playtime, poopscooping, brushing, bathing, going to the vet, etc.
Oh, and there’s the adoption fee at the shelter, which usually includes spay/neuter and at least initial shots.