A lot of the costs really depend on you. What breed you go for (size, pedigree), whether you buy from a breeder or rescue, and whether they're easy to care for (long coat or short).
But there are costs you can't really escape - insurance, vaccinations, flea and worm treatments are vital especially in the first year. Insurance is a must unless you have thousands of pounds at your disposal - vet care isn't cheap and even something as simple as blood tests or a scan can set you back hundreds if not thousands. As a first time dog owner you really need to be enrolled in training - and not just a quick six week course, find a school that has the three stags of obedience training if possible, or even one that encourages weekly attendance. It's fab to help you learn about your dog and of course it's great for their socialisation as pups.
The Doghouse can be quite...scary if you don't have a dog, but I've found the reality is a LOT easier than it was made out to be here. We've got a pedigree beagle - so high-energy but low maintenance in terms of grooming costs. He's four months old now and toilet trained, sleeps pretty much all night, naps most of the day, is healthy and enrolled in puppy classes. He knows sit, lie-down, "paws on the floor" and "toilet". Of course he doesn't obey every time but he's young and he has a lot of growing and learning to do.
It IS a big commitment - in terms of being tied to the house for a bit, not being able to leave the dog alone (so, dog sitters or walkers if you can't take him with you), holidays (kennels here are a fortune per week, and he'll need to be up to do date on all vaccinations including kennel cough, plus flea and worm treatment) and working hours. Will the dog need to be in daycare, or can you work from home/take him with you? If you can take him with you, make sure your insurance covers you for this.
Food costs - well, again it's largely up to you. We buy in bulk and probably in total he costs me about £150 a month. So that includes insurance, flea/worming, toys, chews and all his food. Puppies need lots of chew toys!