Depends where you are in the country re costs. Our dog was £80 from the Edinburgh Cat and Dog Home, and already neutered, vaccinated and chipped. A dog walker cost £10 a day (we needed 3 days a week and someone was home the rest of the time). You may not need a dog walker if someone is in the house or if you work short days or similar.
Insurance started at about £15 a month but we had to claim on it for an accident - ddog spent a week in the vet hospital and we only had to pay the £85 excess, thank god. His actual bill was over £4000, so insurance really is worth it! Premium didn’t go up much, but as dog got older he started to develop other issues (liver issues, which he recovered from) and a lot of insurance only covers a new condition for the first year, so we paid about £70 for pills every 2-3 months until he had fully recovered. Also, horribly, when he had to be put down we were charged for that too (can’t remember how much). In the end the insurance was up to about £35 a month due to his age and various ailments.
Food is up to you - you can spend wildly varying amounts on it from basics dog food to luxury stuff.
You’ll need vaccines - not covered by insurance. Some vets do vaccine deals where they’ll charge you a small direct debit every month and it covers worming, flea stuff and vaccines when they fall due, which spreads the cost.
Lead, collar etc don’t have to be expensive.
Dog sitting is a pain to organise if you don’t have anyone to help out! It’s expensive. My dog hated kennels - was phobic about being back in the pound.
But our dog was an absolute joy and delight —most of the time—. I would have another in a heartbeat if we weren’t out so much. When we got the old dog, DH could take him to work. When his business folded and he worked 9-5 the dog quickly demonstrated that he hated being left for the whole day and we had to get a dog walker quickly. It wouldn’t be fair on the dog to get another one now - maybe one day!