Our two Great Danes cost about $70 a month in food, maybe $80.
Well critter checks and vaccinations, all in for everybody including three cats, run us about $500 a year. The bulk, but not all, of that is for the two dogs so figure maybe $200 per dog.
And on that note, if you get a dog, you probably want to find a country vet. I believe you said you were out a ways now. So, the more rural the vet, the lower the cost. They're also likely, frankly, to be better at what they do. Or at least that's been my experience. Probably has to do with having to be able to treat dogs, cats, cows, horses, etc.
The male cost us $300 as a puppy, and the female $400. Maybe that was the other way around. Anyway, both dogs have papers, but they're specifically "pet grade." That means we won't be winning any prizes at dog shows, as if we cared about that. We got them different places, but each was from a household where the parents lived in the house and were pets, and where they were the only dogs.
As for what they're "worth? " Well, the dogs saved me from a methhead one fine morning about a year ago. They guard the property, and I'm sure they're the reason the house has never been broken into, isolated as it is. Ditto the barn, because their fence runs up to the barn. Finally, love.
Our big boy has hit his senior years, so far without health complications. But they'll happen, and when they do, we'll pay for them. that country vet will help with that, but I'm firmly of the opinion that things like vet care are why we have money.